This 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!
Since posting the above I have run into this error on some other occasions not related to Claims based authentication. Specifically I found this error would occur whenever attempting to save one particular MPP file into a server. In that particular case reviewing the schedule and specifically the resource sheet turned up the cause:
Clearly this resource is corrupted (this is an English install) in some way, what this indicates is that the error 9000 is a generic ‘error of last resort’ it would seem.