NEED HELP WITH CUTOM MP SCENARIOS !

[ChrisMK4]

So i just found out the Armaholic website , wich is very popular for cusstom mods, models and Scenarios. I downloaded a custom map, move the PBO file in the MP folder of the game and when i try to create a private server for my friend, i can't find it. I only see the map when i am in a official scenario and i click server settings. Why i can't see the map when i first try to start a server ?