NET USE I: \\DOMAIN.COM\IDRIVE

I use the above statement in all logon scripts that are run by our users on
our network, but under Windows Vista this does not appear to be successful,
as when I access any of the folders in drive I: they all report "Access
Denied".

If however I map the drive using a server name instead (NET USE J:
\\SERVER\IDRIVE) this is successful.

After having completed both of the above (one in the Logon script and one
manually) and then in a DOS box I type NET USE I see the following...:

Status Local Remote Network
-------------------------------------------------------------------------------------
I: \\domain.com\idrive Microsoft Windows
Network
OK J: \\server\idrive Microsoft Windows
Network

Why am I have such a problem under Vista with the DFS? 99% of the machines
on my network are all Windows XP with SP2, and none are having this problem.

P.S. I have no AV software installed, and I have tried disabling the Firewall.