I am making a denim rag quilt..Top is denim and back is cotton...I am trying to sew the X's on each block using wonderfil accent thread top and bottom and I keep getting shredded thread and rats nests on back. I am using a 100 topstitch needle... I have adjusted the tension..cleaned the bobbin case ...rethreaded...changed my needle and it is still happening... This is a brand new Janome 6600....I am using the dual feed... I sew very slowly over the seams...sometimes it happens midblock where there are no bulky seams...Does anyone know what is wrong here???? Val