I have a 6600 with the FMQ foot and blue dot casing. I too have been doing quite a bit of FMQ lately.
First thing I'd do is take the bobbin out and spool off and totally re-thread the machine. Try your FMQ again but just try moving in a forward straight line. If all is ok, then try left then right then backwards. Try some circles. In other words, gradually move towards full FMQ. Be sure that you put the presser foot down before you start sewing.
If still problems, then I'd switch the foot over to the Accu-Feed (leave in the blue dot) and do some practice quilting stitching. with it Is it stitching OK? If so, then go back to your FMQ foot and go thru the steps above. If prlblems with Accu-Feed, then you know it's not just the FMQ issues.
Top tension may need to be loosened off.
What kind of thread and needle are you using?
And if I get too stymied, I call my dealer and get superb help!
Last edited by QuiltE; 08-07-2012 at 08:46 PM.