I remember having this problem with Windows clients months ago and it seemed to stop when 1037 came out. KF 1037 worked great on Mac too, until this most recent patch that came out yesterday. Everybody on my server has working perks but I am the only one with all level 0's. A fresh restart of KF lets me use my perks in solo and some random servers but I've had a zero-percent success rate on my own server (and a few other random servers). My perks are whitelisted and worked prior to the most recent patch.
Here's what I tried (without success):
-Completely deleting ~/Library/Application Support/Killing Floor/
-Restarting computer, Steam, verify integrity, re-install
-Disabling all perks on my server
EDIT:
Ah I seem to have stumbled upon a solution that actually works after reading almost 100 threads that pretty much said the same stuff. I don't remember what thread so I can't cite it but here's the solution:
"~/Library/Application Support/Killing Floor/Cache/" contains a cache.ini file and numerous other files that end in ".u", in my case. The ".u" files are, I'm assuming but didn't actually check, hashes of the file that was downloaded from a server. cache.ini contains the correlation between the meaningless hash filename ".u" file and the meaningfully-named one. At any rate, I downloaded each of the ".u" files listed in cache.ini and placed them in "~/Library/Application Support/Killing Floor/System/" and my KF install has been good to go ever since.
So from "~/Library/Application Support/Killing Floor/Cache/":
-open cache.ini and leave it open
-delete everything contents of directory
-go to google and download the .u files listed in cache.ini
-throw them into "~/Library/Application Support/Killing Floor/System/"