L4D2 maps error

Hey guys a quick question, for some reason whenever i try to load any of the l4d2 maps in gmod nothing happens. I choose one, click start singleplayer, and it doesnt start the game. It doesnt crash or anything, but it doesnt load up the map either.

Any ideas as to why this might be happening? Could it be because l4d2 and gmod are different versions of source or something? (read that on the forums)

You have to download the modified maps from garrysmod.org

The pure L4D2 maps have unsupported entities (Because of Gmod’s older engine version) that don’t exist in Garry’s Mod, thus making it unable to even load the map.

I don’t think the entities really matter. I mean Gmod can handle maps from other Source mods as well, it just ignores additional entities (all Source engine games do AFAIK). What changed between the different versions is the character to separate two parameters of an input/output. At least that’s what happened to the VMF files.

If you used a comma in a parameter of an input/output in an older Source version map, you wouldn’t be able to open the map again until you fixed that comma with a notepad. That’s why they use a sign that looks like an arrow since L4D1.

That is not all, the maps in L4D2 and later are version 21 (Dota 2 going to have 22). That is why you cannot play on them in The Orange Box