Windows 7: Windows Backup refusing to work with 2nd harddisk

Hello,

I've got a second harddisk installed -- the one from my old computer. With Windows Explorer I can read and write to and from it.

However, when I try to set Backup to use it for storage, I'm getting this message:

"The specified network location cannot be used." Clicking on Details shows:

"The network location cannot be reached."

Network? Why network? This is a harddisk, not a network.

If anyone knows what's going on and could help, that would be very kind.

Thanks,
Ariel

(Windows 7 Ultimate 64-bit)