SP6 was the 'cause' of that bug. You can try SP6a, but SP5 has been proven to work. Some of the tools at SI's support website come with disclaimers against use with SP6. Whether you're physically on a network or not makes no difference as the licensing works over the same protocols - that's where some of the issues are.
If it were my machine, I'd either upgrade to Windows 2000 w SP1 or move back down to NT SP5.
speye