HELP! My top thread on my Mille has suddenly started fraying and breaking. I have changed the needle three times, sanded the hopping foot and two curly thread guides for possible burs, and i am out of ideas or things to try. I just quilted a t-shirt quilt with the same cone of thread so I don't think that is it. I use Superior So Fine 50wt. Anyone know what could be wrong? I am desperate for answers.