I've run into this problem when I used a purchased prewound bobbin. As others have said- be sure you have a good bobbin, or try starting with a freshly wound one. Rethread the machine and insert the correct size bobbin with it unspooling on the left side. If this doesn't work- take out the bobbin holder being Sure you will reinsert it in the right orientation. My 6000i manual is useless for this- no pic of the proper orientation. It is amazing how much lint can accumulate Behind the bobbin holder! My tension is usually about 3 1/2. Good Luck!