Cannot Mount .CBU Full Backup -> Can't Select a Drive Letter

I’m attempting to restore files from a full-disk backup from my old hard drive. Unfortunately, when I go to Manage and Mount, I cannot select a drive letter to mount to. The dropdown list is completely empty. When I mount the drive without the drive letter, the virtual drive shows up in Devices and Printers as VDBUS under storage. When I look in the Drive Manager, I do not see the drive available to assign it a drive letter.

I’m running Windows 8.1 64-bit and Comodo Backup

Is this an issue with the VDBUS.sys driver? With Comodo? I’ve been searching Google, here, Bing, etc. for the past week trying to find out why I’m not given the option to select a drive letter and it’s driving me somewhat batty at this point.

Any help would be greatly appreciated!