WORKAROUND:
1. Click "Spool SQL" instead of OK in the alter job window.
2. Send Script to Editor (4th toolbar button)
3. Comment out the line referenced as the problem in the error.
4. F9 to run.
5. Go back to the "alter job" window and just cancel it.
STATUS:
Waiting for a fix to be released in a future version of Toad for Oracle.