C&C Generals LAN problems

My brother and i both purchased the ultimate C&C collection for the purpose of playing together via LAN.

when we tried playing generals zero hour, we used the direct connect method. 

we managed to create and join each other's game and get the game started.

however, once the game starts, one computer will show the disconnect menu, saying that the other player has connection problems. on the other computer, it will always be stuck at the loading screen, with the loading bar at 100%. 

so we are clearly able to connect to each other since we can enter the same game and start it. but why does this connection problem always occur when the game starts?