Had a similar problem with my Toshiba 5700 DVD player and heat was the cause.
When I had the HD cable box (Scientific Atlanta 3100HD) sits directly on top of the Toshiba, the picture regularly freezes and skips during the 2nd half and near the end of the movies. Apparently the heat from the HD cable box and the DVD player and causes the DVD player to overheat.
The problem completely went away when I provided adequate ventilation in between the units.