I suggest you have it serviced, what could be a disaster if you try and fix it youself could be half an hours work for a trained camera mechanic, and not as expensive as you think.
Mine did this as well. I finally figured out it seems to be related to the film advance wheel. If you don't fully, and firmly advance all the way, it seems to cause this problem. Perhaps there is some sensitive contact that is engaged at the end of the advance procedure???