Any time you feel your library may be corrupted:
Back up the library. Do not replace any previous backup copies, just in case you need them!
From the Tools menu, run the Recover Library operation to rebuild the library. See Recovering a Damaged Library for more information about this command.
Note: Due to a bug in the Macintosh System, you may encounter database corruption when your EndNote library is stored on an SMB (Windows) server, you are accessing it from a Macintosh running OS 10.4.x, and you make changes that require reindexing data. If this should happen, copy the library to your local computer (or a Macintosh server) and run the Recover Library operation from the Tools menu in EndNote.