Have you tried dragging and dropping the files to \Steam\steamapps\common\left 4 dead\left4dead\addons

Also not confusing addons with add-ons?

If that doesn't work try this (sorry it worked on replacing an important file for someone else though they had to do it twice). Right click on L4D2 in your Library > Properties > Local Files Tab and click on Verify Integrity of Game Cache

Hope that does the trick.

It did the trick for my files.I now have all the vpk files for my addons. So thank you for that. : )

Now I have a new problem.... When I load up a level (it doesn't matter which one) I can play for about 5 minutes give or take and then my game glitches and is fine for 30 seconds and it does this about 2 or 3 times then I get my desktop mouse back and the game shuts down, like I never even had it running. >.<" This is starting to frustrate me.

Can't load malformed vpk "c:\program files (x86)\steam\steamapps\common\left 4 dead 2\left4dead2\addons\3431863757.vpk" me sale eso al habrir el juego ayuda porfavor

This thread was quite old before the recent post, so we're locking it to prevent confusion.