I had this same problem once. At the end of all frustrating and unsucessfull 'fixes', I found my problem The thread I had purchased and used sucessfully for half the quilt looked like it was would onto the spool way too tightly during the first half of the manufacturing process. I checked this out by putting on my bobbin winder and watched the spool only while winding the bobbin. Sure enough, the spool would jerk and halt while the thread was coming off it, like it was stuck between the other threads on the spool. I actually can't even use this spool for regular sewing, due to the jerkiness of the thread coming off the spool. Although it cost over $5/spool and I had two of them, I finally decided to toss them. But, cheap as I am, I marked the labels with felt pen and just use those spools now for hand sewing.