Renault Trafic Problem?

I have a Renault Trafic 57 plate
The van cuts out and just throws up the engine stop light, sometimes it will run a couple of weeks without problems and then do it again.
The other day it cut out on the motorway and wouldnt restart I called the AA and half an hour later when the AA arrived the van started up and ran ok.
The fault code it showed was P2101 throttle actuator control motor circuit range/performance
Could anyone tell me what could be the potential cause of this as a local garage didnt seem very confident of finding the problem.
Cheers