I'm so happy that this thread came up. My Janome on a Grace II frame was doing the same thing this weekend. Drove me crazy with all the places I have to go back in and fix with thread tacking by hand.... it's a quilt for our living room so it doesn't have to be perfect. Now I know what to go back and look at and try cleaning to correct the problem. Like mermaid, I had changed bobbins, needles, several times....never once thought of the encoders. Thank you thank you thank you!