It could be that the file systems aren't compatible. Like you, I have two HDDs, one with GhostBSD and one with a favorite Linux distro. GhostBSD uses ZFS while my Linux OS uses EXT4 format.
On Linux I can't open the other HDD to grab files because it doesn't read ZFS. But I can view, read, copy, etc all my Linux files when I'm using GhostBSD.
I had better luck moving files by copying and pasting them to a USB stick (formatted FAT32) than exchanging them between HDDs.