Environment: SP2010 Enterprise, one server with separate SQL

This just cropped up on a server that has been working flawlessly for months. I created an account for a new external user, but when they try to open the site they receive a 401 error before they are even asked to authenticate. I've tried digging through the trace logs but can't spot anything unusual (though I'm not sure exactly what to look for). It is consistent on multiple browsers and workstations, however they are an all-Mac office so there may be variables I just can't account for. I even looked at their "keychain" to make sure there wasn't an entry that might be trying to pass credentials automatically, but I don't see anything obvious.

They are using OSX 10.6 and have tried Chrome, Safari, Firefox and even IE5 with identical results. The site's security is claims-based and does not require SSL, and there are no fancy webparts that require additional security, it's all pretty straight-forward. I happen to have access to a nearly identical machine to what they are using and tried to replicate the situation as closely as possible but had no problems.

Has anyone run into this before? I've only found references to 401 error after authentication, so they don't seem to apply here.

Update: Just tried having them manually enter the site/credentials into their keychain, still getting 401 before it even asks for authentication.

Update 2: I just looked through the IIS logs for the site and found a plethora (apx 400k total from all logs according to WebLog Expert Lite) of 401 entries. After doing some research (and catch me if I'm reading this wrong) the only ones that are errors are the 401 X Y Z where Y (sc-win32-status) isn't 0? In that case there are mostly 2148074254 statuses and a couple (not enough to be related to this problem) 64 statuses. However, it looks like the 2148074254 events happen at any time of day and have skyrocketed in the past month. Does this suggest any clues? Unfortunately IIS isn't my strong suit, so I don't have an intuitive understanding of this information.

  • If they're getting a 401, AuthN has occurred on the IIS side. Can you provide some more details? * What kind of claims based auth? IWA/FBA/SAML? * Have you compared the traffic on working account with the traffic on a non-working account with something like WireSharK?
    – ciphertxt
    Commented Jun 26, 2013 at 17:54
  • Ah so it's an IIS problem then? I have researched that now, see my second update above for the full explanation. Authentication is NTLM. The problem with examining traffic of a non-working account is that the client in question isn't even getting far enough to enter an account.
    – thanby
    Commented Jun 26, 2013 at 18:53
  • helped any solution to you? Commented Jan 18, 2019 at 14:14

2 Answers 2


It is an IIS server authentication problem, not a SharePoint problem. You can put any website on the IIS Server and it still would give the same error. Use wireshark or fiddler to trace the http headers.


Try check if you have disabled LoopBack


On IIS check if you have enabled required authentication mode.

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