Stuck on Marimba ringtone

Hi there

Running itunes 10 and iphone (3GS) software version 5.0.1. Just updated both.

Have custom ringtones synced and they appear in the phone's contacts as the ringtone, but the ringtone is 'stuck' on marimba. Won't play any other ringtones including the pre-loaded ones. When I play the custom ringtones on the iphone, they play. Have tried everything listed in other discussions - re-sync, switch on off, de/authorise computer. Anyone got a different solution?

Many thanks in advance