Error message "Project Server encountered a problem with this error code:9000" occurs

his is a new error that has been bugging me for a few weeks now:

The error message "Project Server encountered a problem with this error code:9000" occurs when attempting to save a project in Project Professional 2007 client:

Additionally you may receive a blank "Job failed" window when trying to check-in a project:

This problem is caused by an Internet Explorer login session to Project Web Access expiring and as a result the project client is forced to re-login, however this re-login only seems to be supported in Project Professional 2010 and not 2007 client running in backwards compatibility mode.

This only applies to Project Servers / SharePoint configured to use Claims authentication, or when Project Professional 2007 is using Forms authentication to logon to PWA. (I assume Project Pro can re-authenticate easily using NTLM)

The best workaround to this is to not use the connect / disconnect and work offline options in Project Professional as this does not re-log you in.

Additionally perhaps avoid opening PWA in a separate Internet Explorer window so as to not logout inadvertently.

Performance problems also exacerbate this issue.

Hope this helps someone!