I found a solution to this thanks to sudodus on ubuntu forums.
Because it seemed hard to find this simple fix I wanted to add it here.
My card reader would not open the 64G card from gopro.
The solution was install "exfat-fuse" and reboot.
"exfat-fuse" was available in synaptic, marked it for install, applied, and it installed.
Rebooted and card reader worked.