I upgraded the firmware on my m600i last week using the update service application and now all of a sudden I cannot get audio transferred to my stereo bluetooth headset. I get a error "The bluetooth device is not authorized for this audio stream". My headset model is Creative CB2350.

I called Sony Ericsson and they say that third party headsets are not guaranteed to work and they couldn't tell me any specifics about the firmware update. The same headset works fine with a Nokia 6086.

Has anyone else had this problem ?

I actually experienced the same problem with my w950 and SE's own HBH-DS970 bt headset. Not sure this will help you but all I had to do was to unpair the headset from the phone (e.g. delete it from the phone), restart the phone, reset the bt device and pair it again.