Outlook meeting requests do not show resources in invitation when sent to/from XP SP2 clients

[Dag]

A = Win XP SP2
B = Win XP SP1
C = Win XP SP1
Server = Exchange 2003

We are experiencing that when A sends a meeting request to B & C and also
invites a meeting room as a resource, B & C do not see the resource in the
invitee list or the location. (meeting rooms are set up to automatically
accept if not booked)

When B do the same C can see the location, A can't.

In a Win XP SP1 enviroment this works without faults

any suggestions?