Sticky now time movement

Friday, during a session with a client, the now time line movement began to jerk forward in small increments during play back.  I sound was ok, but the now time movement was jerky.  I restarted Sonar and it was still bad.  I apologized to the client and rebooted the computer.  That took care of the problem and it hadn't done the same since.  I am concerned though.
 
What might have happened?
 
Thanks,
 
Tom