This has happened to me too, but I really try and have all the shakes. This is a balanced diet and very very important to follow it to the letter. I am only on Day 6 this time and hit ketosis y/day I think. I know that last time I did this diet, someone posted that they had collapsed and had to have an o/n stay in hosp. because of phosporous levels (I think). Scared me to death and so I try to squeeze in each shake, even if I have one late at night. The other thing is I think it makes you more hungry and thus more likely to break it altogether. I did Lipotrim for 3 months last time and I felt wonderful by just following it to the letter and losing at a huge pace.
You need to have all your shakes otherwise you arent getting enough vits and minerals! Your body will actually store fat if you dont have enough food...this is a very carefully controlled doet where you have as little cals a day as your body can stand without going into complete starvation mode...MISSING SHAKES WILL MAKE YOU ILL!!!!