Hi,
When you boot in WinPE there is no AD to get the correct time from and if the time is off so the computers use the time from the BIOS. If the time is not correct the Network Access account cannot login and access the packages and the self-signed ceritficate
used byt the PXE could be invalid as well depending on how much time difference there is.
Regards,
Jörgen
-- My System Center blog ccmexec.com -- Twitter
@ccmexec