Can't add shared folder

I have a Xen 8.1 VM running OMV 5.0.5 and am having trouble accessing a USB drive. Specifically, the drive is 12 TB and is partitioned (GPT) into two volumes (each EXT4). The disk shows up correctly under "Disks" in OMV, and I am able to mount the volumes under "File Systems". The problems occur when I try to create a shared volume. I've attached a couple of screenshots. (The log files don't show anything of note).

The drive itself seems okay if I mount it on a separate Linux laptop without going through OMV. The folder "Video2i" exists.

Where am I going wrong?

Thanks
Eric

I also noticed the following message as the OMV VM boots up. Again, the disk seems to work fine on a Linux Mint 19 laptop.