And what did you find? How did you free it up?
Don't just blow by something like that, you may be ignoring a clue. The two reasons I can think of for this would be water intrusion due to clogged vents (happens all the time) or mice urine.

And my point is, if you had water intrusion, then you may have water damage under the carpet, passenger side. Yank up the carpeting, GET IN THERE, and look around. Any way water got on the transmission control module? (If yours is an auto). Remember, any compromised module can play hell with the CAN bus.