It’s payday and your employees are waiting for their payment, but Aspel NOI refuses to stamp the CFDI payroll receipts. The system displays cryptic errors, the PAC rejects the vouchers, and the clock keeps ticking. This is one of the most stressful scenarios for accountants and payroll administrators in Mexico. In this article, we will resolve the most common CFDI stamping errors in Aspel NOI, from certificate problems to incorrect tax data.

The Error

When attempting to stamp payroll receipts in Aspel NOI, the system may display different error messages depending on the root cause:

  • “Error al timbrar el comprobante” (Error stamping the voucher) — a generic message that can have multiple causes
  • “301 - XML mal formado” (Malformed XML) — the receipt’s XML file contains data that does not comply with the SAT schema
  • “401 - Certificado no vigente” (Certificate not valid) — the digital seal certificate (CSD) has expired or been revoked
  • “402 - Sello mal formado” (Malformed seal) — the voucher’s digital signature is not valid
  • “CFDI33179 - RFC del receptor no está en la lista de RFC inscritos no cancelados del SAT” (Recipient’s RFC is not in the SAT’s list of registered, non-cancelled RFCs) — the employee’s RFC does not exist or has been cancelled in the SAT registry
  • “NOM1001 - El RFC del receptor no coincide con el registrado en el complemento de nómina” (Recipient’s RFC does not match the one registered in the payroll complement) — discrepancy between receiver data and the complement
  • “Error de conexión con el PAC” (PAC connection error) — communication cannot be established with the Authorized Certification Provider
  • “El complemento de nómina no cumple con la versión requerida” (The payroll complement does not meet the required version) — the complement version is lower than 1.2

These errors typically appear when running the bulk stamping process from Procesos > Timbrar recibos (Processes > Stamp receipts) or when trying to stamp an individual receipt from the preview.

Root Cause

CFDI payroll stamping can fail for several reasons. The most frequent are:

Expired or revoked digital seal certificate (CSD). CSDs are valid for 4 years. If not renewed in time, all stamping will be rejected. The SAT can also revoke a certificate due to tax irregularities.

Incorrect employer tax data. The issuer’s RFC, legal name, and fiscal postal code must match exactly with the records at the SAT. With CFDI 4.0, the SAT strictly validates this data: even a difference in capitalization or accent marks causes rejection.

Invalid or unregistered employee RFC. Each employee must have their RFC registered and active with the SAT. If an employee has an incorrect RFC, an unauthorized generic one, or has been removed from the registry, the PAC will reject their receipt stamping.

Outdated payroll complement version. The SAT requires payroll complement version 1.2 for CFDI 4.0. Older versions of Aspel NOI may generate receipts with complement 1.1, which is no longer accepted.

PAC connection problems. Corporate firewalls, proxy servers, antivirus software, or simply an unstable Internet connection can block communication between NOI and the stamping provider.

Incomplete employee data. Fields such as CURP, social security number, employment regime type, and work schedule type are mandatory in payroll complement 1.2. If any field is missing or has an incorrect format, the XML will not pass validation.

Step-by-Step Solution

1. Verify the digital seal certificate

Open Aspel NOI and navigate to Configuración > Datos de la empresa > Certificados digitales (Configuration > Company Data > Digital Certificates). Check the expiration date of the loaded CSD. If it has expired:

  1. Log in to the SAT portal with your e.firma (FIEL)
  2. Generate a new digital seal certificate
  3. Download the .cer and .key files
  4. In NOI, remove the old certificate
  5. Load the new .cer, .key and enter the private key password
  6. Save the changes and perform a test stamp with one receipt

2. Validate the employer’s tax data

Download the company’s Constancia de Situación Fiscal (Tax Status Certificate) from the SAT portal. Compare field by field with the data registered in NOI (Configuración > Datos de la empresa / Configuration > Company Data):

  • Issuer RFC (13 characters for legal entities, 12 for individuals)
  • Exact legal name (no abbreviations, with accent marks if applicable)
  • Fiscal address postal code
  • Tax regime (must match the SAT code)

3. Review each employee’s data

Go to Catálogos > Trabajadores (Catalogs > Employees) and verify for each employee:

  • RFC — must be 13 characters and match their SAT certificate
  • CURP — 18 characters, valid format
  • NSS — 11-digit social security number
  • Regime type — correctly selected according to the SAT catalog
  • Contract and schedule type — mandatory fields for complement 1.2

To validate RFCs in bulk, you can use the SAT’s RFC validation service or request each employee to provide their updated Tax Status Certificate.

4. Check the PAC connection

Navigate to Configuración > Timbrado > PAC (Configuration > Stamping > PAC) and run the connection test:

  • If it fails, verify that your Internet connection is working properly
  • Check that the Windows firewall is not blocking aspelnoi.exe or the PAC port
  • If you use a proxy, configure it in NOI’s network options
  • Confirm that your PAC credentials (username and password) are still valid and have not expired
  • Contact your PAC to verify that their service is operational

5. Update Aspel NOI

Download the latest update from the official Aspel website. Before updating:

  1. Back up your NOI database
  2. Close all NOI instances on the network
  3. Install the update on the server first, then on each workstation
  4. Open NOI and go to Ayuda > Acerca de (Help > About) to confirm the version
  5. Verify that the payroll complement is version 1.2

6. Retry the stamping process

Once the issues have been corrected:

  1. Go to Procesos > Timbrar recibos (Processes > Stamp receipts)
  2. Select the receipts pending stamping
  3. Run the process and monitor the progress
  4. Check the stamping log to confirm all receipts were processed
  5. Receipts with errors will be flagged — review the individual error detail for each one

Specific Errors and Their Solutions

Error CodeDescriptionSolution
301Malformed XMLCheck for special characters in names or addresses. Update NOI to the latest version.
401Certificate not validRenew your CSD on the SAT portal and load it into NOI.
402Malformed sealVerify that the .key file and password are correct. Regenerate the CSD if the problem persists.
CFDI33179Recipient RFC not registeredAsk the employee for their Tax Status Certificate and correct the RFC in NOI.
NOM1001RFC mismatch in complementVerify that the RFC in the employee data matches the CFDI recipient.
Connection errorCannot contact the PACCheck Internet, firewall, and PAC credentials. Try again at a different time if the PAC is overloaded.
Invalid complementIncorrect complement versionUpdate NOI to generate payroll complement 1.2 compatible with CFDI 4.0.

Prevention

To avoid stamping issues during payroll periods, follow these practices:

  • Renew the CSD in advance. Keep a record of the expiration date and renew it at least 30 days before it expires.
  • Validate tax data quarterly. Request updated Tax Status Certificates from your company and employees at least every 3 months.
  • Stamp test receipts before closing. Generate a test receipt at the beginning of each period to detect problems before payday.
  • Keep NOI updated. Install Aspel updates as soon as they are available; many fix stamping bugs.
  • Document PAC credentials. Store the username, password, and contract expiration date with your PAC in a secure location.
  • Keep a backup of the CSD. Store copies of your .cer and .key files in a secure location outside the main computer.
  • Review the stamping log after each process. Do not assume all receipts were stamped; check the log to detect individual rejections.

Summary

  • CFDI stamping errors in Aspel NOI are usually caused by expired certificates, incorrect tax data, or PAC connection problems
  • Always verify the digital seal certificate validity before each payroll period
  • Employer and employee data must match exactly with the records at the SAT
  • The payroll complement must be version 1.2 for CFDI 4.0; update NOI if necessary
  • Test the PAC connection and check the firewall, proxy, and credentials if there are communication errors
  • Validate tax data proactively to avoid rejections on critical paydays