IIS - the request is rejected by HTTP filter when there are european char in the url

Question

I'm using a web api application that returns valid post-codes for given city. The application is hosted on WinServer 2008 R2, IIS 6.1.

Application works fine as long as there are no European-char (ä,ß,æ,ø,å) in the URL. But with any special/European-char in URL I get the following error message:

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

E.g. for working URL: edu.web/Api/PostCode/Heidenau

E.g. for non-working URL: edu.web/Api/PostCode/Heidehäuser

E.g. for non-working URL with URL encoding: edu.web/Api/PostCode/Heideh%C3%A4user

How to configure the IIS to accept european chars?

Thanks.

Solution

I've resolved the issue by involving our system administrator. All Internet requests are passed through ISA server (Microsoft Forefront Threat Management Gateway) which by default filters all requests with special characters before they hit our Webservers.

After we changed the Configuration, everything started working as intended.