Funny how things happen! I just answered this kinda, down below in the "flush 7 & 8..." thread, lol. We must be psychic!
I have had failures, too. I think it has more to do with what I've been eating the few days previous to the flush, my stress level at the time, and other things like that. Before I started bowel and liver cleansing, I just ate normally and has some good flushes. After starting, I got wrapped up in eating less, taking all kinds of supplements and "worrying" about doing it all perfect, trying to reconcile all the different information and different things people do. I wasn't eating much if any food, just doing psyllium and green drinks and enzymes and probiotics... all the other stuff people mention.
Now I'm trying to "just relax about it" and eat better. So I have a little steak or hamburger every night. Steamed salmon and slop butter all over it. Eggs fried lightly in lard or butter. Spinach with butter on it. Animal fats, in other words. Veggie oils are fine, but you need animal fats. I know that flies in the face of all the marketing out there, but when I do what they say I feel like crap after two months. When I listen to my body, not other people, I feel great. You do need to have a certain amount of oils in your diet, or your flushes will be "duds." You NEED oil (in the days before the flush) to create the bile that flushes things out. If you've been eating nothing but "rabbit food" and paranoid about oils, there will be no bile in your system to flush anything out with. You can flush and flush, and nothing will happen except taxing your liver for no reason. Just relax and look at these other things, that might not be quite as obvious. It's been working for me. :)