try a different paper.
I just started using staples brand "picture paper" ($10 for 30 sheets)
(you can get it on staples.com if you don't have a local store)
it's amazing. the traces transfer very easily, and the paper doesnt stick to the iron. the toner sticks SO WELL with this paper that you can literally take a toothbrush to the board after to finish removing the paper, rubbing about as hard as you want, and not damage the traces.
simply amazing. I was using epson glossy photo paper before, but I had 3 failed transfers in a row on one board, because it was quite complex with lots of fine traces. First try with this paper it transferred perfectly except some traces were blobbed into each other, this was because i put so much pressure on the board when ironing.
I tried again, using very little pressure, and it came out pretty much perfect.
trust me, you won't be disappointed.
the paper is a little more work to remove, as it doesn't peel off in one piece like some others, you just have to soak it for a while and keep peeling off layers, and at the end you can use fingers/toothbrush/whatever to scrub off the remaining thin layer of paper. it's definitely worth it though.