Machine stops ''for safety reasons''

Question

I am trying to sew 5" squares together for a quilt using the special foot that makes a perfect 1/4" seam. I am using a straight stich (Memo 02) in which the needle is to the far left. Every so often (I never know when) the machine locks up and reads "Machine stopped for safety reasons".I then have to re-thread the machine. When the machine stops, it jerks the thread out of the take-up lever.