I would think it might be the way its threaded or it could have some lint in it in the thread path. I have a Brother Ovation and I can use any kind of thread, regular thread, aurifil, quilting, wooly nylon, metalic, very heavy thread, etc and I've yet to have a problem. Most of my "serger" thread comes from Hancocks or Tidewater sew n vac, but I have a variety to use. If you have a manual and go thru it again and double check your threading and see if it allows you to open the part where the thread path is to see if something is clogging it. I love my serger. Right now, I'm making a log cabin with fleece and its going so well. When its done, I'll use the wave stitch to finish around the outer edges. Do you have anywhere close to you that can help, like a sew n vac or dealer.