I've had this issue a couple of times with my iPhone 4 and U310. Both occurrences followed some erratic plugging in/disconnecting of the iPhone by yours truly (call came in, didn't want to use BT). Anyway, I was able to clear the condition by disconnecting the phone, performing a 'hard reset' on the iPhone (hold Home and Power buttons together until you see the Apple logo) and power cycling the car/head unit. The hard reset will kill any conflicting background functions in the phone's OS that could be the source of the U310 sending Format Read errors. YMMV.
