TOCA3 is somewhat problematic to backup. There is currently only 1 known way to make a 100% working backup.
(Finally) found the link:http://forums.xbox-scene.com/index.php?showtopic=492703
yes, it's 23 pages. Read it. It will explain everything you need to know. Note that now that dvd2xbox has an ISO ripper, you should be able to use this instead of ISO ripper app. But I'm not sure if anyone tested it. If you do, please tell WiSo (current author of dvd2xbox) so he knows it works. He was interested to hear from anyone who had tried it.
This link should really be in the "Important Threads" sticky, under "Game Specific Backup". Mods?