I would really focus on the bobbin thread. What kind of machine are you using? I have a Janome and it is very fussy about the bobbin being threaded correctly. Are you using a walking foot for stitching in the ditch? If not, that might also be why you are having trouble. Hope someone here can help you solve your problem.
Originally Posted by vjengels
Chances are it's the bobbin thread that's getting tangled, check that you have the correct bobbin for your machine, as well as rethreading the machine. if that doesn't help you may need to adjust the bobbin tension