I'm having some trouble with my DIY cruise control but the symptoms are similar to yours.
It's a very recent retro fit but I know that it works because the light was on today and I was cruising along happily.
Flicked it off, came around for another pass up this decent A-Road and nothin, no light and no more cruising.
I plugged the vagcom cable in and did some digging around - found this out about mine, may help you..
Regardless of clutch position my switch remains in the operated position. I removed the switch from above the clutch pedal, took about 20 seconds, is just undo cable and twist switch to remove ( my lower panels were still removed from the fit which may have helped ).
I noticed immediately that the switch was rattling, ordered a new one for £13 and I am hopeful that it will cure the problem.
Will post back when it's fitted. Worth a look dude, might save a bunch of cash.
Good luck!