On the Tools tab you can lock/unlock Projects or Project Reports:
When a project is locked it can not be edited and when a project's reports are locked no reports can be generated for the project. Locking can be done manually or it can be done via Workflow Rules.
When a project or its reports are locked you will see the lock icon next to the project in the Project Explorer:
Projects and their reports can also be unlocked from the Tools tab within the Project Editor:
A user must have permission to lock/unlock projects or project reports.