Hi Steve Q.
Thanks very much for the info.
With a little investigation work i sussed out how to get the panel off and access the regulator. I found out that it was one of the wires in the regulator had a bit of corrosion on it and one of the strands had snapped causing it to coil up and jam instead of sliding through the cable sleeve. Everything else looks fine so it looks like a new regulator should solve the problem.
Cheers
Steve