Mine stopped working a couple of years ago. Took it to my mechanic, who had the tester unit, all seemed fine when the tester was in place of the ECU, so no switches or mechanical problems. We put the ECU back in after all the messing about, and it's worked fine ever since.
The ECU for it is up under the dash, fairly easy to get to by taking down the liner under the steering wheel (RH Drive)
Maybe a quick wiggle about would help.
There are two switches on the brake and clutch pedals that are supposed to disengage the Cruise when you press either one, maybe one of those switches is signalling wrongly?