Error when setting up a project

when one of my users goes to set up a project in the PSA module they get the following message when changing the name of the project in the project wizard:

Warning:

Project cannot be created as the asociated invoice project 3600 no longer exists.

When other users in the same security group set up a project they do not get this message they can set up a project without any problems.

Any ideas??

The warning says that - the Project Contract what you are attching to the project does not exists.