Please see if its file system is exFAT, as drives greater then 32GB usually come pre-formatted in exFAT. And it seems MX5 doesn’t support reading/writing in exFAT.
If it is exFAT, then you’ll have to format it in FAT32 filesystem.
Use guiformat tool for this in windows.
After formatting, MX5 should be able to mount and read/write the drive