Try running a recover on your file and see if you get the same error with the recovered copy. (Try this even if recover does not report any problems).
Things to keep in mind about Recover:
While Recover almost always detects and fully corrects any problems with your file...
- The recovered copy may behave differently even if recover reports "no problems found".
- Recover does not detect all problems
- Recover doesn't always fix all problems correctly
- Best Practice is to never put a recovered copy back into regular use or development. Instead, replace the damaged file with an undamaged back up copy if this is at all possible. You may have to save a clone of the back up copy and import all data from your recovered copy to get a working copy with the most up to date information possible.
And here's a knowledgebase article that you may find useful: What to do when your file is corrupt (KB5421).
It appears to have worked. I'll play with it for a while and report if any other issues occur. Thanks so much for the 'right' suggestion.
I suspect file damage because your reported error message: This action cannot be performed because this file is not modifiable.
Isn't consistent with then being able to modify data in the file as you have reported. A file with permissions locked on the file would trip that error just by attempting to modify data. If a password on the database file were the cause, you'd get a different error message.