I had someone test my map for coop (as i dont have many people to play waw with) and they said that when playing coop the non-host player cannot earn points through damaging or killing zombies. I googled around and found no fixes. The player could still gain points from powerups like nukes and carpenters. Also in coop the other player is not visible. If you need to test for yourself i can pm you the link to the map.

Do you have the latest version of mod tools?

Yes. I haven't seen the problem for myself as I haven't had a friend to test it with. Going from what someone who tested it for me has said.

Maybe test it yourself? Maybe your friend has that error? Or did he test it on your computer? That's really weird as that never happens very often. It may be that your map is broken. Does the point system work on your other maps? Am I correct?
edit:I forgot that you said he tested it on coop. Yea your map has to be broken, I think some files are corrupt.