Cruise control will automatically disengage if it's not able to maintain within about +/- 8-10 MPH of the desired set-point speed. It will also automatically disengage if the vehicle's shock sensor thinks you might have hit something, which means a really bad pothole can make it disengage the cruise control.
Something obviously happened that caused the CEL to light up, and hopefully it stored the code so it can be read by your mechanic. I don't think using the cruise control "caused" the problem, though.
:)):)
