Remove the negative lead from the battery, wait 30 secs and reconnect and see if the fault remains. Removing the negative lead will re-set the computer and may cure the problem. If not, I would guess that the problem is sensor related.
I have successfully used this trick when the car refused to start in heavy rain and it is definitely worth a try as it is very quick and easy to do and there is no downside to trying it.
I'll keep my fingers crossed for you.
