That isn't really an issue with the ZIP we put together. That's just Left4Dead 2 being a dumb ass. Valve has a broken Download Table, so new people can't download the scripts needed to join.
The way I got mine to work was to send them this link and told them to move the Addons, Cfg and Scripts folder to this folder.
X:\...\Steam\steamapps\common\left 4 dead 2\left4dead2
Although, I myself have taken it out since I got annoyed with people raging at the sight of the Riot and Knife (followed by crying about mods or hacks), then leaving causing my Versus to end. But when I had it on, which was like... 2 days ago or so, it was working fine.
Also, Brian, could it just be another plugin interfering with this one?