Memtest is completely independent of Windows and its drivers - that's precisely what makes Memtest invaluable.
Memtest is reliable on 2GB, you don't need any other test, and you don't need any other attempt as long as Memtest sees errors.
Every Bios I know has some kind of "default settings" for the Ram. This is always the start value for any timings adjustments. Also, your Bios has a "default settings" for the complete Mobo, which could be a good idea.
I haven't tried if the ep45-ud3r reacts cleverly with a single Ram module, though I expect it does. Check in the Bios adjustments that it's not forced on "Dual-channel".
If you still get errors with all default settings, try other slots on your mobo, try to clean the module's contacts with a rubber and the mobo with a brush. Then, you may test your Ram on another (someone else's) mobo.