I have to know what brand of machine it is. I've only had trouble with the bobbin case when I didn't "click" it in. On 2 other machines with the drop in type bobbins--they are very fussy if any lint or even a tiny piece of thread works itself into the path. One of them does have a little wiggle room when trying to line up the bobbin race. Poorly wound bobbins, thread jumping off the takeup lever and the thread coming out from the needle guides cause most of my problems. The only one I couldn't figure out or fix on my own was when a lint ball got sucked up into the tension disks on my computerized, auto-tensioning Elna and I couldn't figure out how to get to the tension assembly to get at the lint. Now I'm a little OCD about keeping the lint from accumulating on the needle bar. I couldn't finish the quilt for 2 weeks and was $70 poorer because of a little lint ball.