Hello everyone, first post here!

I tried searching for this topic but i didn't find anything that helped me, so here goes:

i am trying to play in custom maps online with a friend of mine from the Unit 22 Shoppa Compilation, v1 pack which i downloaded with the game client, but every time i try to load a game it won't late me; the loading stops and i receive an error message about loading up another copy of the map.

How can i solve this and play on custom maps? Thanks a lot!