Shouldn't be as I run G6 without any problems at all on XP pro with SP1 and all updates installed.
That said could make sense to re-install your server just in case anything has been changed by the install of SP1.
Maybe also see if you can grab a trial version of G6 as changing server client may help.
If I can find a link later will post back OK.
EDIT:
http://international.tucows.com/prev...-001-007C.html