This behavior occurs when the web service is not configured for Integrated Windows authentication (or access restrictions have been implemented at the ACL level), and there is an issue with the IUSR account or its password has been changed.
Ensure that Integrated Windows authentication has been enabled for the web service in IIS if applicable
Ensure that ASP.NET, Authenticated Users, and Internet Guest Account all have Read permissions to the parent folder and containing files of the associated web service
If the above items appear to be in order, then there may be a problem with the Internet Guest Account. Steps may need to be performed to reconfigure and re-sycnhronize the IUSR and IWAM accounts and their passwords
To Reset IUSR password:
Steps from 3rd party website to resolve IUSR account issues:
1. Open AD Users & Computers. Expand the Users OU, right-click on the user account (iusr_servername/iwam_servername) and select 'Reset password' to reset the password. Note: the password can't be blank.
2. Open this User Account's properties and make sure that 'Password never expires' and 'User cannot change password' are selected.
3. Open IIS from Administrative Tools.
4. Expand servername>Web Sites
5. Right-click on 'Default Web Site' and select Properties.
6. Go to the 'Directory Security' tab and click the Edit button under 'Authentication & Access Control'
7. Enter the new password you just reset for the IUSR_servername account and click OK.
8. Enter the password again to confirm and click OK.
9. Click OK.
10. Open a command prompt and run IISRESET
11. At the command prompt, enter the following commands:
2) c:\inetpub\adminscripts adsutil SET w3svc/WAMUserPass “password” (Where password = the password you entered for the IWAM_servername account in AD Users & Computers)