I have had this exact same problemwith my Bernina 640 skipping stitches. Talk about frustrating! I wonder if it could be because I used a basting spray on the quilt, which I didn't use on my practice samples? I just got my machine back from the dealer, and that is 80 miles away in the city--not an easy trip for me. It worked great for a while and then started skipping again. You just never know if it is going to work or not work.