A new user that was able to log on successfully, but when he goes to advanced search gets a userid/password popup to re authenticate. when he fills it in he gets a message:
Error: Existing credentials are not valid, please enter new credentials ...
He had been logged on to Web Viewer, but closed that, and still gets the error.
This was caused by not signing off from one access method before going on to a different one.
The problem was resolved when signing off.