Q for dvd users, I have noticed some areas where my abs dvd appears to skip a section, for example, in the All Step section, where Cathe starts working her obliques, all of a sudden after 2 she moves on to something else, but very smoothly, not like a skip. I have a feeling it is a problem with my dvd or dvd player. I checked the disc and it does not appear to have any scratches or dirty spots, any suggestions? Thanks!