Corruption can occur in databases.
Recover is an option in File Menu in Filemaker
This is not a best option, Save a Copy As under the FILE Menu or Recover under FILE menu are options.
When a database is performing well, Save As Copy is a RECOMMENDED thing to do.
The saved as copy can be a Clone (without records) or COPY with current records.
If you do not do this, you are allowing for disaster.
Hmmm....what kind of disaster? We host the database elsewhere, and a copy is saved every night. That doesn't seem to make a difference with these non-deletable scripts. Recover sounds scary.
Recover is pretty safe. It's just not "best practice" to then turn around and use the recover database. Recover makes changes to your file and there's no guarantee that the changes were all made correctly. Recover's number one priority is to get the file into a state where you can import all the data from it into a undamaged back up clone. Making the file reliably useable, is a secondary priority.
Save a copy, with the compressed options selected has been used by some to fix minor issues with a database file. I doubt it'll work in your case but you have nothing to lose by trying.
I'd try to find the most recent backup copy that does allow you to correctly delete scripts, save a clone of it and then import data from the damaged copy into this clone. If all else fails, there are ways to rebuild the file one structural component at a time that doesn't force you to go completely back to square one.
Recover will drop invalid blocks and fill them in temporarily just so that you can get your file open and export out the data. That is why it is not recommended that you go forward with a recovered file.