Error Code: 500 Internal Server Error. The request was rejected by the HTTP filter. Contact your ISA Server administrator. (12217)

WORKAROUND

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work around this issue, configure the Web publishing rule so that it
does not block high-bit characters. To do this, follow these steps:

1.	Start the ISA Server Management tool.
2.	Expand ServerName, where ServerName is the name of your ISA Server computer.
3.	Click Firewall Policy, click the Web publishing rule that you created to publish the Exchange Server computer for access by OWA users, and then click Edit Selected Rule.
4.	Click the Traffic tab, click Filtering, and then click Configure HTTP.
5.	Click to clear the Block high-bit characters check box, and then click OK two times.
6.	Click Apply to update the firewall policy, and then click OK.

obtained from: http://support.microsoft.com/default.aspx?scid=kb;en-us;837865