Congrats this is a great mod! glad to see your hard work paid off. I too will say I would love to see the co op version updated, this mod is really a perfect example of what I have been looking for to play with my friend.
you can fix the issue by changing placed units with the rpg7 (gp) to the rpg 18 for the time being. If you go into the virtual arsenal and try to add the rpg 7 (gp) you will get the same error.
forgive me if this is on my end, when i try to place troops with the rpg7 (gp) or view the weapon in the arsenal, i get this error "Cannot open object cup\weapons\cup_weapons_rpg7\rpg7_launcher_loaded.p3d