Sonar LE stuttering during recording.

Hi,
I've been using Sonar LE for a good few years with no problems, but suddenly, every time I record something the recording stutters at random points during the recording. You can hear the metronome skipping beats or suddenly slowing down and then picking up the beat again. Has my Sonar gone senile?
Any suggestions to cure this would be very welcome as it is impossible to record now.
Thanks in advance.