While configuring the SharePoint 2010 for Forms Based Authentication, I encountered above error. To get the problem, I had to change “IncludeExceptionDetailInFaults” to true somewhere. But WHERE?
Here is what solved my problem:
Go to following path:
1. C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\WebServices\SecurityToken
2. Open Web.config there.
3. Add following in the “behaviors > serviceBehaviors > behavior” node.
Now try to login and see what error it gives, off to a next error