1998 Chevy Monte Carlo Camshaft Position Sensor Circuit Ran

I was driving down the road a city road going 25 miles an hour when my service engine light came on. Nothing out of the ordinary had happened prior to it popping on. Luckily my mechanic was 3 blocks away. The mechanic pulled the code and it is the Camshaft Position Sensor Circuit Range/Performance. What would cause this to go off? I have never heard of such a thing. I don't have that many miles on this car. Not really, for the age of the car. I would just like to know what would cause it to go off, what does this indicate and what, if anything, could go wrong next. This car has really been trouble free for me and now I'm starting to wonder if it isn't going to nickle and dime me to death.