Cant play any mod maps! ( Alcatraz ect )

[frplymstr]

Everytime I try and play any map that did not come with the original disc, the game loads OK but when I click on join map, the game crashes back to my desktop.
I tried all the different fixes that other threads said, but still doesnt help.

Does anyone have any idea what I can do so as to play these new maps.

P.S. : I play in single player.