This can occur for a variety of reasons. One workaround that can sometimes work is choosing Edit->Undo and then try saving the project again. It may be necessary to undo several edits in order to successfully save the project.
- A project file is located on a network or shared drive
- The project name or the name of an imported media file contains a symbol such as &, %, $, *
- One of the media files has been moved, deleted, or renamed
- A recently added media file is corrupt
- The project file is damaged or corrupted
- Always keep media and project files on a local hard drive
- Avoid symbols in file and folder names
- If you have moved media files on your system, move them back to their original locations. To move projects to a different computer, save the project as Standalone.
- If the project can't be saved after importing a media file, try temporarily moving or renaming just that file
- Restore from a backup copy of the project, such as from a Time Machine backup