Can't access workstation via Remote Web Workplace

Hi everyone,

This is an important and urgent request hence the 500 points offered.

I administer a small network running SBS 2003 R2 with 5 workstations attached. The workstations all use XP Pro with SP2. Everything runs well locally and all client PC's are happy accessing domain resources etc. The staff often leave the office and work from their homes and utilise Remote Web Workplace (RWW) to log into their work PC's. This has worked well for the past 4 years or so - no problems at all.  However things have changed. Recently, one office workstation was replaced by a Win7 Pro machine, and another system was upgraded to XP SP3 as part of the 'trying to keep current' policy, albeit we are slow in doing so ¿.  Here then is the problem we have: the staff who log in from home to their XP SP2  machines are all fine - everything works great as it always has done. The staff member who logs into his Win7 Pro machine from home is fine, but the staff member who logs into their recently updated XP SP3 box cannot. She selects her name from the RWW list of computers to connect too, as per usual, but is somehow then presented with the Win7 Pro's PC login screen! (weird). Again, everything works perfectly fine locally at the office. It's when they go home we have the problem. If she tries to use her credentials to log on regardless, she receives the error ..."To log onto this remote computer, you must be granted the Allow Log on through Terminal Services Right....etc"  ... But it's crazy that she doesn't see her own computer log on screen any longer.  It's feels like it's a name resolution has gone weird on the SBS2003 server- but nothing has been changed on the Server. I am suspecting it's the XP update to SP3 that's the issue, but have no idea what to do next.

Any help would be greatly appreciated!
Thank you
Paul C