I had the same problem on my 9020. Fixed it by unscrewing the right side panel of the printer (4 screws, 2 from the back, 2 from above). Inside, just below the level of the carriage, I found a sliding thing that should be able to move back and forth along most of the length of the printer. This was stuck but could quite easily be loosened. I slid it back and forth a few times, and then the carriage was able to move normally again.