Perhaps there's a source involved? Check to see if one of the sources are doing it. i.e. Delete a source, try it, delete another source, try it again, until you are down to 0 sources. (Though you may want to duplicate your scene before doing this if you want to preserve the data). It would be very unusual if it "stopped working". I'm guessing you mean it froze. Could you guys also include a log file as per the instructions in the link anyway?