"HTTP Error 401.1 - Unauthorized: Access is denied due to invalid credentials" error message w (4336018)

While trying to access the Archive Manager website which is set to use Forms authentication, the following error is displayed:

HTTP Error 401.1 - Unauthorized: Access is denied due to invalid credentials

If failure auditing for logon events is enabled, a failure audit will be generated in the Security event log for the IUSR account.
This error does not occur if the website authentication mode is changed to Windows Integrated.

• The user account does not have the required user rights to access the Web server.
• The user account is disabled, locked out, or expired.
• The wrong user name or password is specified in IIS.

1. Click Start | Run
2. Type secpol.msc
3. Navigate to Local Policies | User Rights Assignment
4. Check that the local machine IUSR account has the "Access this computer from the network" right
5. Ensure that the local IUSR account and the Guests security group are not assigned to "Deny access to this computer from the network"
6. Close the Local Security Settings MMC.
7. Click Start | Run
8. Type compmgmt.msc
9. Open System Tools | Local Users and Groups | Users
10. Double click the IUSR account
11. Check the account password is not disabled and is not locked out, or expired
12. Right click the IUSR account and change the password
13. Open IIS Manager
14. Right click the ArchiveManager website | Properties
15. Directory Security tab | Authentication and access control | Edit
16. Change the password to match the password entered in step 12
17. Ensure only "Enable anonymous access" is ticked and click OK
18. Click Start | Run
19. Type IISRESET

For more information please see this Microsoft knowledgebase article: http://support.microsoft.com/kb/909887