Hi Mark, can you run a search for the file, and see if it is checked out by another user? If it is, you will not be allowed to check it in, EPDM only allows you to check in files, that are checked out by you. Unless you are the Admin user, in which case you can check in other users checked out files.
1.- finds that there is a file already registered pdm with the file name you want to register .
2.- check that the file does not have it in possession another user.
3.- Reset the server Pdm for reconstruction files system.