This happens to me alot lately... i'll feel the shift into that heavier state of dreaming and I end up losing my grip on that state and waking out of it. The only way I can get past it is to keep slipping back into that state again and again until I finally wake up in a LD.

It takes me anywhere from 3 -6 times of trial and error to slip into a LD lately. I think the mind eventually gets the idea of what I want to do and it relaxes enough to let the cross over happen. I think this difficulty arose because I've messed up my sleep schedule severely for the last few weeks. I know that if I can get it back on track I'll slip into WILDs much easier.

Maybe try adjusting or creating a sleep schedule to stick to?
Just a thought.