XP pro - cached domain login problems

I run a windows 2000 domain controller (root, DHCP, DNS)
from which NT 4.0 and Windows 2000 professional
workstations are authenticated to network resources
without problem.

My problem arrises with XP professional; from a fresh
install and all service packs / fixes added I then add the
workstation to the domain without problem, set the number
of Interactive Logins to cache to 0 *(explained below) and
reboot;

once rebooted I then sucessfully login to the domain as a
standard valid domain user that is able to access
resources as defined in Active Directory; after a
subsequent reboot XP pro is no longer able to find the
domain controller WHY ?

n.b * XP pro doesn't warn users that they are being logged
on using cached information (increasing error discovery
times !!), so when cached logins is left on default of 10,
so when the domain controller cannot be contacted as I am
experiencing , my users just become to realise that
printers and file shares are unavailable etc only when
they try to access them.

I have done the same install and cache settings procedures
as described with the XP installations but on windows 2000
professional without problems ? .... so why can XP pro no
longer see the domain controller ??

All comments and sugestions are much appreciated