Interesting problem. I wonder if it would be possible to just phone a local service person and get his/her advice over the phone without having to pay for a servicing/repair of your machine? And is there a toll-free number that you could use to ask the manufacturer of your machine about the problem?
Also, I know from experience that if you don't pull your bobbin thread to the top before you start quilting that you're likely to have problems--and hold both threads towards the back until you've gotten a few stitches in.
Good luck!