The bobbins for the two machines are very different, The bernina has a jumbo bobbin and the viking has the little old plastic bobbin. I just can't figure it out. I have stitched on different machines for 40 years and this problem just seems to happen out of the blue. I have rethreaded everything, changed needles, reviewed the manual, checked my feet. It just won't behave. I really think there is some kind of glitch with the machine going on. Maybe one of the computer cards, or maybe something with the thread cutter although I don't use the thread cutter.