Looks like there are many users with similar problem...
I also have the same problem in copying large files from internal HDD to external USB devices (flash disk and portable HDD). The copy process start and then halt after a while, then a restart is needed.
My 2 other computers, Dell 600m and Asus EeePC 1000HE (both are using Windows 7 Prof 32), do not have this problem.
My affected computer is Acer M5641 (Q6600, nForce, Windows 7 Ultimate x64) and already installed latest nvidia nforce chipset 15.37 and 15.46.