Attempting to use the NX remote desktop client to log onto a Linux Mint server results in the error 'Failed to load session "ubuntu"'. This can be fixed by editing the
/usr/NX/etc/node.cfg file, and changing the CommandStartGnome to the following:
CommandStartGnome = "/usr/bin/gnome-session --session=gnome-fallback"
After this, run:
/usr/NX/bin/nxserver --restart
Logging in using NX will now give you the Linux Mint Gnome Classic desktop.