Do you have a networked system, where different computers are accessing the same bin, from different projects, at the same time? Avid has a built in safety mechanism – if multiple users are accessing the same bin, only the first user can save the bin. The second user will only have read only access to the bin. So, try closign the bin in the new project (and any other project the bin is open in) and see if that helps.
Another option – .pmr is a database file. These corrupt all the time. Try quitting out of avid and deleting the database files. Next time you boot up avid, it should ‘scan’ media and rebuild new database files.