I have this problem with my sewing machine. It is a Brother XL-5130, so it has no bells and whistles. It will sew with a regular foot just fine, but as soon as I put on the darning foot in order to quilt, the bobbin thread will not catch, or may catch every 5-6 stitches, so I get these long sections of just loose top thread. Any thoughts as to what needs to be done to fix this? I have re-threaded both the top & bobbin threads and re-attached the darning foot several times to no avail. Thanks for your help!