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FIX: HTTP Error 401.1 – Unauthorized: Access is denied due to invalid credentials.

By Jesse | June 11, 2009

We have encountered several issues all caused by the same problem :

When on a sever, if you try to browse to a page on that server, you get a 401.1 error after being challenged several times.

Every time this was caused by denial of a loopback request.  To test to see if this is your problem, add this registry key, then reboot the server. The registry key to add is :


Add to this key a DWORD set to 1


then reboot.

If this does not fix your problem a number of other things to try.

  1. Many devices can cause problems in the network path, make sure the server is acutally throwing the 401.1 and not a proxy server.  To do this goto the IIS logfiles in c:\windows\system32\logfiles.   Check the log, find the request and verify the server returned a 401.  If it’s in the log here, you are definitely hitting the server.
  2. Watch the traffic.  Try using a tool like httpAnalyzer ( to view the network traffic.  You get a 15 day trial with the download.
  3. Try  a tool like Microsoft’s AuthDiag …  It will allow you to simulate requests to the site and verify various permissions and authorizations are actually working.
  4. Verify credentials on the file.  Make sure the ACL’s on the actual file are correct and that you do really have access.
  5. Try turning on basic authentication and see if the problem goes away.  This can sometimes be a valid workable solution as long as the site will always be hit via SSL.  As long as you’re using SSL, there is no risk in turning on basic authentication because everything is traveling in the ssl tunnel.
  6. If none of the above work.. feel free to post and we can see what we can think of.
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Topics: Uncategorized | 4 Comments »

4 Responses to “FIX: HTTP Error 401.1 – Unauthorized: Access is denied due to invalid credentials.”

  1. Wayne Says:
    October 14th, 2009 at 3:39 pm

    Hey nice tip. The Registry fix worked for me.

  2. Jonathan Says:
    October 28th, 2009 at 11:08 am


    I had been fighting this issue for several weeks and tried all of the available M* fixes and nothing worked.

  3. Jim Says:
    October 5th, 2011 at 10:13 am

    Thank you, exactly what was needed.

  4. James Says:
    August 3rd, 2013 at 4:28 pm

    If none of that works, which happened for me, this is a possible fix

    Right Click on My Computer > Manage
    Expand the users
    Select the IUSR_whatever user and right click to set password
    Set a new password for this account
    Go to IIS and Right Click on Web Site node > Properties
    Flip to the Directory Security Tab > First EDIT button
    Enter the new password you set for IUSR_whatever and then Apply and out.
    Should work.