While I don not have an 8900, let me see if I can help you out here.
If not, we have a ton of talent in our forums so one way or another we'll find a solution.
If you select another Sound Profile from the default list of profiles, will the ringtones change for your contacts?
My second question is when you performed the upgrade, did you backup your device using Desktop Manager?
**Edit** I renamed your thread so other members would see that you were needing help with your device.
When you Edit the contact for whom you have set the custom ringtone for, when you scroll all the way to the bottom, it says "Custom Ring Tone:" right? If it does, just highlight it, press menu, and select Delete field. Then save the changes.