Same here, we removed AT&P, installed RT and got the same error. Also, we don't see the old prefixes or are unable to add new ones to a forum.
Do you have an advice to solve this? This is currently on a testserver we we try the upgrade from 4.4.10 to 4.5.4.2 so we shuld be able to "fix" it on our own 😉
Thanks!
Update: We restarted the upgrade from scratch, this time we kept AT&P installed (but deactivated) when installing RT but no change, we see the same error.
Chris