Your top tension may be too tight. Loosen off and try another design.

jmcl1954,
I had the same problem. I have a Brother Innovis 2500D. My service rep said to turn the small screw on the bobbin case a little bit. I did this, and it fixed the problem! He said that the screw has a tendency to loosen with use. I hope that this helps you!
auntbaba

You can either tighten the bobbin tension or preferably loosen the upper tension and leave the bobbin tension alone if it is normally OK

First I would loosen my top tension. Only adjust the bobbin case tension if your attempts on top do not work, because it is a super duper headache if you get the bottom off and can't get it back. (ask me how I know) Also see my hint under the reply of auntbaba. Use a permanent ink marker.

I have had the problem several times . I adjust the tension. And sometimes I take out the bobbin and rethread. I also find that when the bobbin has a small amount of thread on it this sometimes happens ( I change to a new bobbin and everything is fine.) Hope this helps a flower for you . Good Luck

jmc, by now you know which it was - top or bobbin. Heheh! *4 each of you.

I think you got your answer for this - I was told when I got my machine that if bobbin thread shows on top it is the tension, and vice versa with the mess on the bottom. don't know how true that is, but I sure hate the messy tops and bottoms, don't you?

That happens to me once in a while when the top thread get caught so that it does not feed correctly.

These ladies are good, but I would let the technician make the adjustment. I agree with jrob, if you mess it up, you would have a heck of a time getting it back to normal. Our machines need a undo button like our software.