Primavera v8.1 Client - Messages saying that another user is in the schedule

We have a bug where Primavera thinks that another user is in the schedule, when there is not.  It's been 6 months and no one can seem to figure out what to do.

When someone tries to F9 schedule, they get the "You have opened the current project(s) in Shared mode. Other users currently have the project(s) open..." message.  Users can't delete a schedule or assign as a baseline, because it gives the message that another user is currently in it.

Anyone ever experience this? Any help is much appreciated.

Thanks,

Jon