Probably a dumb question, but are you sure you're entering the passkey code correctly? My friend with an E46 had all sorts of trouble pairing again after a dealer service on his car. Nothing worked, and he was getting very frustrated. We finally took the trunk liner out to look at the ULF module, and whaddaya know? He had transposed two numbers on the passkey. When he got them in the right order it paired on the first try. His response was a classic Homer Simpson "Doh!"
Dave