After talking on by phone for a few minutes, I often now get a message saying "Press OK to transfer call from the headset to the phone", followed by an error code. I don't have a headset and the device is not currently connected to any Bluetooth device. Does anyone know what's wrong?
You didn't say what phone you have. Was it connected to a bluetooth device? Is it possibly searching for one?
Try pulling the battery while the phone is on, and then restart it after a few minutes. That solves a lot of problems, amazingly!