Hi,
Sorry for not helping much on this, been away mostly due to lack of internet.
For RPG-X to load correctly you need a few extra parameters to be in the shortcut you use to start the game.
If you have the shortcut that the installer created for you on your Desktop, please try launching the game via that.
If you don't, right click the EXE in the install location select 'Send To' and then 'Desktop (create shortcut)'. With that new shortcut, right click it and select properties. In the target line, go to the end and outside of the double quotes ", paste the below in.
+set fs_homepath C:\Program Files\The Last Outpost RPG-X Ultimate Edition +set fs_game RPG-X2 +set vm_ui 0 +set vm_game 0 +set vm_cgame 0
Once you have done that it should look something like this:
G:\Program Files (x86)\The Last Outpost RPG-X Ultimate Edition\quake.exe" +set fs_homepath G:\Program Files (x86)\The Last Outpost RPG-X Ultimate Edition +set fs_game RPG-X2 +set vm_ui 0 +set vm_game 0 +set vm_cgame 0
Note, I have my RPG-X installed on another hard drive which is why it's on G:\, I've renamed my EXE to quake.exe, and I have a 64-bit system so it's in my 32-bit program files folder (x86). Based on your last post yours will be on your C:\ drive and in your program files folder, not the (x86) one.
After you've done that, attempt to launch the game from that shortcut you've just created and then try and load the map.