I was told the same thing about not exercising strenuously. I used to go to the gym 5 days a week. Since I started IP I have been going 2-3 times a week and have stopped most of the weight training. The first few weeks were really hard probably because of the reasons above (not enough carbs). But now that I am more adjusted to the diet it feels fine.
I have noticed that if I work out the day of my weigh-in my numbers aren't as high, but I think it is just because my body retains water....