The first time I had that happen it turned out I had missed a step in threading the bobbin. The second time it happened was when I was using "bobbin" thread. I have the Husqvarna Topaz 20 and it does not work well with the very fine bobbin thread. I asked my dealer about it and he told me to bring it in and he could check it and make adjustments but I figure that it was not that big of a deal. I prefer to use the same thread in the top and the bobbin.