Project cannot be saved with the same name

Need your help;

I have a project file residing on the project server 2003 (SP3) which have been using it for sometime. Couple of days ago, a team leader modified the file as usual but couldn't import it back to the project server using Project Professional 2003with the same name. An error pops up stating:
"You cannot overwrite the default version (Published) of a project. To save this project, type a new project name or save the project as a version other than the default".
This is unusual since we all have to update tasks and resources in order to keep up with the changes on the baseline. This was done in the past all the time but now it just won't do it. The project file is not visible through Project Center nor through Project Web Access. After searching around, it looks like there is a ghost file on the server which cannot be seen. Any idea how to remove the ghost file in order to save the project under the same identity?

Any suggestion?

Thank you

Project cannot be saved with the same name