What service pack is installed in the x64 machine? if you have sp2 you can try that hotfix if they have one for x64 architecture. Also try the SP3. I never had that problem with xp64, but my network cards were always realtek. You can also try unchecking tcp/ip 6 in those properties, it would only be a bandaid and not a solution, maybe even see if there is an updated driver on marvel's website. Go to their website, not the manufactures of your computer.