pezi5499 - I fixed this bug this morning - http://open.silverstripe.com/changeset/71345/modules/sapphire/branches/2.3/forms/RequiredFields.php . It will be in tomorrows daily build if or you can apply that change to your code.
I had the same problem when running dev/build on the upgrade. It turned out to have been caused by lowercase table names.
To clarify, I had the issue when upgrading on my development machine, which is a Macbook--but I had copied the database and files over from a Windows machine, which had converted the table names to lowercase.
I replaced the database with a correctly capitalized copy from the live site, and then everything worked fine. The upgrade went smoothly on the live site.