Make sure you have downloaded the last update to FTMaker (FTM version 21.0.0.723). It addressed most of FTM's memory problems with large files. If you already downloaded the update then I suspect corrupt media files (if you're telling FTM to compact - and - back up the Media files). You can tell which media files are corrupt by clicking on the Media Tab and looking for any media file icons that are NOT displaying miniaturized pictures of the file. You'll need to delete and replace those media files with clean copies. If that doesn't work, then I suspect your main .ftmb file may be corrupt.