Error; after checking bobbin threads, press start...

Question

Why does my memory craft 9000 keep stopping after 5-6 seconds of manual stitching culminating in an error message - after checking bobbin threads, press start button?
It continues to do this indefinitely.
It has been a good machine for 7 years (or more) enjoying much success with embroidery and normal sewing but wonder if it is wearing out?
Has any one else had or overcome this problem.