When HR or payroll staff attempt to import affiliate movements (registrations, terminations, and salary modifications) into the IMSS SUA system from an external file, it is common for the system to partially or fully reject records with messages such as “Error al importar archivo de movimientos” (Error importing movements file), “Registro con formato inválido línea X” (Record with invalid format line X), or “NSS no encontrado en la base de datos” (NSS not found in the database). This error blocks timely reporting of movements to IMSS and can result in fines if not resolved within the five business day deadline. In this guide you will find the exact causes of each error and detailed steps to fix the file, import successfully, and prevent future rejections.

The Error

When attempting to import an affiliate movements file in SUA, one or more of the following messages may appear:

“Error al importar archivo de movimientos” (Error importing movements file)

This generic message indicates that SUA could not process the file. It generally appears when the file format does not match the structure expected by the system.

“Registro con formato inválido línea X” (Record with invalid format line X)

SUA identifies a specific line in the file that does not comply with the expected field lengths, separators, or data types. The “X” indicates the line number with the problem.

“NSS no encontrado en la base de datos” (NSS not found in the database)

The Social Security Number (NSS) of one or more workers in the import file does not exist in SUA’s local database. The system cannot register movements for workers that are not in its roster.

“Movimiento duplicado” (Duplicate movement)

The file contains a movement (registration, termination, or salary modification) that was already captured previously for the same worker, same type, and same date.

These errors appear in the Afiliación > Importación de movimientos (Affiliation > Movement Import) window of SUA, immediately after selecting the file and running the import process. Depending on the configuration, SUA may reject the entire file or partially import only the valid records.

Root Cause

Importing affiliate movements into SUA requires the file to strictly comply with the IMSS format and business rules. The most frequent causes of rejection are:

Incorrect file format

SUA expects a plain text file (.txt) with fixed-length fields separated by the pipe character (|). Each record structure must follow this order:

FieldDescriptionLengthExample
Registro patronal (Employer registration)IMSS employer registration number11 charactersA1234567890
NSSSocial Security Number11 characters12345678901
Tipo de movimiento (Movement type)08=Registration, 02=Termination, 07=Salary mod.2 characters08
Fecha del movimiento (Movement date)DD/MM/YYYY format10 characters05/03/2026
SBCBase Contribution SalaryVariable456.78
Tipo trabajador (Worker type)Worker type code1 character1
Jornada (Work shift)Work shift type1 character0

A valid record looks like this:

A1234567890|12345678901|08|05/03/2026|456.78|1|0

The most frequent format errors are:

  • Using CSV instead of TXT with pipes: Files exported from Excel as CSV use commas as separators, which SUA does not recognize.
  • Including headers: If the first line contains column names (“NSS”, “Fecha”, etc.), SUA tries to process it as a record and fails.
  • Incorrect field lengths: An NSS with 10 or 12 digits instead of 11, or an incomplete employer registration number.
  • Extra spaces: Spaces at the beginning or end of a field, especially after copying and pasting data.

Character encoding issues

SUA runs on legacy Windows technology and expects files with ANSI (Windows-1252) encoding. Files saved in UTF-8 (the modern standard) can cause errors when they contain:

  • Accented characters in worker names (á, é, í, ó, ú, ñ).
  • The UTF-8 BOM (Byte Order Mark), which adds three invisible bytes at the beginning of the file and corrupts the first record.
  • Unix line endings (LF) instead of the Windows line endings (CR+LF) that SUA expects.

NSS does not exist in the local database

SUA validates each NSS in the file against its local database (SUA.MDB). If a worker is new and was not previously registered in SUA, the system rejects their movement. This frequently occurs when:

  • New workers are hired and the registration import is attempted before adding them to SUA.
  • The SUA database is out of sync with IMSS and is missing workers that do appear in IDSE.
  • There are data entry errors in the NSS (a single changed digit invalidates the entire number).

Duplicate movements

SUA detects duplicates when it finds a movement in the file with the same NSS, same movement type, and same date as one already existing in the database. This happens when:

  • A file that was already processed is imported again (accidental re-import).
  • The movement was manually captured before attempting the bulk import.
  • The file contains repeated lines due to an error generating it from the payroll system.

Date errors

Out-of-range dates or incorrectly formatted dates cause rejections:

  • MM/DD/YYYY format instead of DD/MM/YYYY (common in payroll systems configured in English).
  • Future dates not allowed for certain movement types.
  • Dates earlier than the minimum period accepted by SUA (generally the current and previous two-month period).

Step-by-Step Solution

1. Back up the SUA database

Before any import operation, protect your data:

  1. Close SUA completely.
  2. Navigate to C:\CobranzaSUA\ (or the path where you have SUA installed).
  3. Copy the SUA.MDB file to a backup folder with the current date, for example: Respaldo_SUA_2026-03-05.
  4. Confirm the copy was successful by verifying the file size.

2. Validate and fix the file format

Open the movements file in Notepad++ (or any plain text editor that displays control characters):

  1. Check the encoding: In Notepad++ go to Codificación (Encoding) in the top menu. If it says “UTF-8” or “UTF-8 BOM”, change it to ANSI from Codificación > Convertir a ANSI (Encoding > Convert to ANSI).
  2. Check line endings: Go to Ver > Mostrar símbolo > Mostrar fin de línea (View > Show Symbol > Show End of Line). Each line should end with CR LF (both characters). If you only see LF, go to Editar > Conversión fin de línea > Windows (CR LF) (Edit > EOL Conversion > Windows (CR LF)).
  3. Remove headers: If the first line contains column names, delete it.
  4. Check the line indicated in the error: If SUA indicated “formato inválido línea X” (invalid format line X), go directly to that line (Ctrl+G in Notepad++) and verify:
    • That all fields are separated by | (pipe).
    • That the NSS has exactly 11 numeric digits.
    • That the employer registration number has 11 alphanumeric characters.
    • That the date is in DD/MM/YYYY format.
    • That the SBC uses a decimal point (not a comma).
  5. Remove blank lines: Check that there are no empty lines at the end of the file or between records.

3. Verify NSS numbers against the SUA database

For “NSS no encontrado” (NSS not found) errors:

  1. Open SUA and go to Afiliación > Consulta/Modificación de trabajadores (Affiliation > Worker Query/Modification).
  2. Search for each rejected NSS. If it does not appear, you have two options:
    • Register the worker: Go to Afiliación > Alta de trabajadores (Affiliation > Worker Registration) and enter all their data (NSS, name, CURP, RFC, registration date, SBC).
    • Update the roster from IDSE: Log in to the IDSE portal with your e.firma, download the active insured workers file, and update your SUA database.
  3. If the NSS does exist but has a different digit in the file, correct the file to match exactly the 11 digits registered in SUA.

4. Remove duplicate movements

For “Movimiento duplicado” (Duplicate movement) errors:

  1. In SUA go to Afiliación > Consulta de movimientos (Affiliation > Movement Query).
  2. Filter by the bimester and year of the period you are importing.
  3. Note the movements that already exist (NSS, type, date).
  4. Open the import file and delete the lines corresponding to already captured movements.
  5. Save the file and retry the import.

5. Import the corrected file

With the file validated and clean:

  1. In SUA go to Afiliación > Importación de movimientos (Affiliation > Movement Import).
  2. Click Examinar (Browse) and select the corrected TXT file.
  3. Select the movement type to import (registrations, terminations, or salary modifications, as applicable).
  4. Click Importar (Import).
  5. Review the results report generated by SUA:
    • Registros procesados (Records processed): Total number of lines read.
    • Registros aceptados (Records accepted): Movements imported successfully.
    • Registros rechazados (Records rejected): Lines that still have errors, with details on the reason.
  6. If rejected records remain, repeat the correction process for those specific lines.

6. Verify the import

After a successful import:

  1. Go to Afiliación > Consulta de movimientos (Affiliation > Movement Query).
  2. Filter by the current date or the imported period.
  3. Confirm that each registration, termination, and salary modification appears correctly.
  4. Verify that the SBC amounts and dates match what was expected.

Alternative Solution

If the import file continues to generate errors after multiple corrections or if there are only a few movements, there are two viable alternatives:

Manual entry in SUA

For small volumes (fewer than 20 movements), capture directly in SUA:

  1. Registrations: Go to Afiliación > Movimientos afiliatorios > Alta (Affiliation > Affiliate Movements > Registration) and enter each worker’s data.
  2. Terminations: Go to Afiliación > Movimientos afiliatorios > Baja (Affiliation > Affiliate Movements > Termination), select the worker, and record the termination date and reason.
  3. Salary modifications: Go to Afiliación > Movimientos afiliatorios > Modificación de salario (Affiliation > Affiliate Movements > Salary Modification), locate the worker, and update the SBC.

Manual entry completely avoids file format issues, although it is slower for large volumes.

Direct submission through IDSE

The IDSE (IMSS Desde Su Empresa — IMSS From Your Company) portal allows you to submit affiliate movements without going through SUA:

  1. Log in to https://idse.imss.gob.mx/ with your e.firma (formerly FIEL) or IMSS digital certificate.
  2. Select Movimientos afiliatorios (Affiliate Movements).
  3. You can capture individual movements or import files directly to IMSS.
  4. IDSE validates NSS numbers against the central IMSS database in real time, eliminating NSS not found errors.
  5. You receive an immediate acknowledgment of receipt with a confirmation folio number.

IDSE is especially useful when you need to submit urgent movements and do not have time to fix the SUA file.

Prevention

To avoid recurring errors when importing affiliate movements:

  • Standardize file generation: Configure your payroll system to export movements directly in the format SUA expects (TXT with pipes, ANSI, DD/MM/YYYY). Document the export parameters so the entire team uses them.
  • Keep the worker roster up to date: Before each import, sync your SUA database with the active insured workers list from IMSS through IDSE.
  • Maintain an import log: Record which files have already been imported with the date and number of records. This prevents accidental re-imports and duplicates.
  • Validate before importing: Open the file in Notepad++ and check the encoding, separators, and structure before loading it into SUA. The 30 seconds of review save hours of correction.
  • Perform daily backups: Schedule a Windows task to copy SUA.MDB automatically every day. A fresh backup allows quick recovery from any problematic import.
  • Train your team: Make sure everyone who generates movement files knows the exact required format and SUA validation rules.

If you experience other errors when working with affiliate movements in SUA, these are the most common scenarios:

  • “Error al conectar con la base de datos” (Error connecting to the database): The SUA.MDB database is damaged or locked by another process. Close all SUA instances, compact the database with Microsoft Access, and retry.
  • “El disco de pago no incluye los movimientos importados” (The payment disk does not include imported movements): Movements were imported correctly but do not appear in the fee calculation. Verify that the movement dates correspond to the two-month period you are calculating.
  • “Error en la estructura del archivo de pago SIPARE” (Error in SIPARE payment file structure): After importing movements and calculating fees, the SIPARE file is generated with errors. This may be due to invalid SBC values imported in the movements.
  • “Certificado digital vencido en IDSE” (Expired digital certificate in IDSE): If you choose to submit movements through IDSE and your e.firma is expired, renew it on the SAT portal before attempting submission.
  • “Movimiento extemporáneo” (Late movement): IMSS accepts late movements (more than 5 business days after the event), but applies a late filing flag that can result in fines. Import your movements within the legal deadline.

Summary

  • SUA rejects import files due to incorrect format (CSV instead of TXT with pipes), encoding (UTF-8 instead of ANSI), non-existent NSS in the local database, or duplicate movements.
  • Always back up SUA.MDB before attempting any bulk import.
  • Use Notepad++ to verify ANSI encoding, CR+LF line endings, pipe separators, and DD/MM/YYYY date format before importing.
  • Register new workers in SUA before importing their movements, or sync the roster from IDSE.
  • For few movements, manual entry in SUA is faster and free of format errors.
  • IDSE allows you to submit movements directly to IMSS, validating NSS in real time against the central database.
  • Submit affiliate movements within 5 business days of the event to avoid late filing fines.