Windows Vault - SharePoint 2010

I have seen a problem where a user always prompts for a username and password when they are trying to open a SharePoint 2010 site. The credential dialog box has got the username field as READ ONLY.

The reason for the prompt is that the username for unknown reason is wrong and cannot be changed!

If you check the security event log, you will see Event ID 4648

To fix this problem you need to check the Windows Credential Manager, start it from the CMD

control /name Microsoft.CredentialManager

and remove the wrongly assigned credential to the site