Vista Reboots At Login Loop

Setting up new HP Laptops with Vista I have come up with an issue of
Vista rebooting while logging in.
This is happening on 4 laptops and only occurs when the users is
attempting to login off the network. As long as the laptop is plug
into the network it will login just fine but as soon as you remove
from network and attempt to reboot in a standalone using cached
credentials it reboots. Sometimes the laptops will come back with
access denied then simple reboot. If you let the laptop sit there
after a reboot it will just sit at the Welcome Screen.