I am having the same problem. Same OS, same chipset, same driver, different motherboard (Asus P6X58D-E)
When I turn on my external SATA I drive, it is not even recognized by Windows. If I go into the Intel Rapid Storage Technology program and click on the icon to run a hardware scan, the drive will appear. However, still no way to remove the drive when I am done. Perhaps a problem with the 64-bit driver?