This is actually really hard to test, unless you do have a very old Moodle around. Anyway, this is the correct testing procedure. I must admin that I could not be bothered to do it myself: 1. Install Moodle 1.4. 2. Create a quiz, attempt it as a student. Perhaps complete one attempt, and leave another one in mid-attempt. 3. Upgrade to 1.9, which probably involves going via 1.6 and Unicode upgrade. – Keep a backup of this Moodle site in this state, so we can repeat the test if necessary. 4. Upgrade to 2.1. Verify no errors occur. Verify that when you review the quiz attempts, it all looks OK. If there are any problems, go back to the 1.9 backup, and see if the problem was in the upgrade 1.9 -> 2.1 or earlier than that. If it was earlier than that, it will be deeply depressing. Alternatively, we could just hope that Henning Bostelmann (who reported the bug) is able to test these changes for us.