out of memory or resource error when connecting to certain outlook mailbox's

Question: on certain users mailbox's when trying to open from an exchange 2007 server via outlook 2003 on an xp pro machine i get the following message  
  can not start microsoft office outlook, unable to open the window, the set of folders could not be open, out of memory or system resources, close some windows and try again.

it is definatley not a pc resource problem (p4 dual core 2gb ram) and other users can log on to the machine fine, the user can log on to other mailbox's but no one else can log on to that mailbox, if tried as administrator it constantly asks for admin password to log on and does not seem to accept it.  this effected one mailbox for the last week but today 2 others are displaying the same problem.
any advice greatly appreciated
ps
it will work on my 8gb exchange server running outlook 2007 and on terminal server clients but not standard xp machines (the mailbox is relatively small btw)