Strange. Before you attempt to fix it, make sure you have a backup.
One possible cause is that your database is corrupted.
From a command prompt, run: suneido -check
One way to fix it would be to unzip the original files to a different directory. In that directory, from the command line, run: suneido -dump persistent
Copy or move the resulting persistent.su to your original director and in that directory, from the command line, run: suneido -load persistent
Note: This will wipe out your persistent set – open windows, contents of workspace, etc. but all of your other tables, including libraries should be there.