Mini 2003 oil light at tick over.

I had my mini cooper r50 53 plate service a few years ago and the oil light came on at tick over. They changed the oil filter and all was well. Now two years later I have the same problem. Changed the oil filter and no change. It was perfect before the last service. Is this a common problem and what should I do now. Anyone else had this. The car has only done 60,000 and runs perfectly.