Selespeed System Failure

[c0w3h]

I am having a problem on my 147 selespeed, it keeps coming up with the message selespeed system failure, and limits me to reverse, neutral, 1st and 2nd, and limits my revs to 4500. However, if i stick my foot down and give it some, then the error goes away, also, if i hold the revs right at the limit then again the error will go away and allow me to change into 3rd. I have checked the oil levels, and changed the battery for a new one, but so far no luck. The aa have been out to have a look at it, but tthey couldnt do anything, he could only check the ecu for error codes but there was none.
Does anybody have any other ideas waht can be causing this issue?
Thanks