Rare and Sporadic 401 Unauthorized Error with ASMX / WCF Web Service Using Windows Authentication
We have a hybrid WCF and ASMX web service currently being used for a decent sized project. Now, most of the time everything works fine, however, on rare occasions and seemingly by accident, the web service starts blocking calls that return 401 Unauthorized errors back to the page in question. It looks like it is the ASMX service calls that are causing this, but given that this does not happen often and is not reproducible, I cannot say for sure.
The error went away after IIS reset, and at least once it just went away in the end. We use Windows Authentication as the Anonymous Disabled Credential Type.
Anyone have any ideas on why this might be happening?
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The solution we finally figured out was a small registry change to disable loopback validation, which is causing IIS registration issues. We actually had this registry edit floating around, but eventually forgot about it.
The key is located at:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa
Add a DisableLoopbackCheck
DWORD with a value 1
and it seems to take care of the problem
MS Support: http://support.microsoft.com/kb/896861
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