From the error message in the title, one of the fields of the table has a validator that is either finding the field value already in the database (I'd suspect the title, subject, or name field ). For a table I had that I wanted to update an entry, but failed the uniqueness check (because of the entry in question, of course), I had to find a harmless modification of the field. (It was a URL, and I add "#DUP" to the end of it.)
I'm also using sqlite3 for that db, and I don't know if other DBMs fail the uniquess check when its because of the record you're updating, but may be worth exploring that.
/dps