I don't know what the problem is. I too was working on a FSL design today and it was over 16,000 stitches into it (29,500 stitch design) and I got a rats nest and had to scrap it so I figured misery loves company*

I have also been there. I was doing a Santa head a while back about a 3 hour job 2 hours into it and it screwed up. I have not been brave enough since to attempt it again....Hope your luck gets better.

What brand of machine do you have?

Maybe if you used another sheet of WSS? Or a better brand? I had that problem and started using Tulle (sp?) netting under 2 layers of WSS. Worked like a charm!

i was using a double layer of WSS. The expensive thread you buy at the sewing center.
It did it again today. GRRRRRR The sewing center asked if I had broke a needle lately as there might be a burr on the pressure foot, or plate. Sure enough there was a burr. So I filed a little with an emery board and was able to get through the project. When i have time, I'll take it in AGAIN and have it fixed.
Thanks guys for all your help.
Cracker