Whenever you start stretching and exercising muscles you haven't used in a long time, soreness is expected. If you feel sore muscles after doing the program, that's okay.

You may even feel soreness in deep muscles around the hip joint.

What you don't want to feel is SEVERE soreness that makes it difficult for you to function. If you encounter that, you'll want to reduce the intensity of the exercises you're doing or choose different exercises. For example, if you do squats and your butt and legs are sore the next day, that's okay. If they are SO SORE that you can't walk, then you should reduce intensity.

You also don't want to feel soreness in muscles that you didn't work.

For example, if you stretched your hamstrings, and that made your anterior hip sore, that means you should probably adjust your hamstring stretching. You may have been pushing too hard and too deep. If you are already flexible in your hamstrings, then you may want to stretch the quads, the hip flexors, and/or the adductors instead.

Remember that the soreness should come from the muscles you worked, not other muscles.