My Ruby uses everything; including Essential Threads. Are you using the same thread in the bobbin and are checking to make sure it's threaded right in top and bottom and you might need to check your needle. Maybe sulky doesn't have a problem with needle but the other thread does. I'm just throwing things out there. I normally use Aurifil but since getting the Ruby I've been using all kinds of embroidery thread, the essential threads and coats and clark and even serger cone thread and haven't had a problem. You can even try putting the spool in a cup behind the machine; some times that also helps. Good luck with it.