Hi Martin,
This is one of the new "features" of the MOSS 2007 Forms Services. If the form has code it requires an admin deploy. A true pain in the patootie if you ask me. Anyway, hopefully you can summon the admin gods for some enlightenment... you could also check your log file - look for a post from David Airapetyan for info on the location of that. Cheerios!
Patrick Halstead
Project Manager at Qdabra