I had the same problem with intermittent abs/service light coming on, this happened after I took the car to a garage to have the clutch replaced. I had a local mechanic look at it and he connected a diagnostic unit to the computer and it showed as a sensor fault on the off side front, which seems strange as the nearside front is the side that had to be dismantled to work on the clutch. He checked both sensor cables, all was ok, he reset the computer and all was well for about 2 months then it started again, went through the same procedure and again it lasted for a couple of months and showed again. The only thing we can think of is there maybe a bad earth connection since the original garage put the car back together.
The car is a 2004 1.9 laguna
alan, February 2014