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I have a site I am configuring to support forms based authentication in SharePoint. I am stuck because I get a 401.5 error (unauthorized) when the login page is displayed.

Any tips for getting started in the debugging process?

I already know that 401.5 means an ISAPI Filter has told IIS the request is not authorized.

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up vote 0 down vote accepted

May be related to Wildcard Application Mapping, or non-standard Application Mapping.

Some good troubleshooting ideas here:

HOWTO: Diagnose 401.x HTTP errors on IIS

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FYI, issue was caused by login page code behind and custom ASP.Net module that was trying to access SharePoint via SPContext.

Even though the code was using "RunElevatedPrivlage" the thread was not allowed to peak at the SharePoint data.

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