Problem: Client Unknown to auth
Solution: add seta net_master0 "192.246.40.28:27650" to an autoexec.cfg in your q4base and/or mod directory.
Problem: MAX_PURE_PAKS (128) exceeded
Solution: You need to remove some unused pak files. The Quake 4 engine can only reference 128 pk4 files at any one time.
This article is under development. I started this because 2 people I play with had these errors tonight. As I think of more errors I will keep adding them. If you have an error that you don't know how to solve, post a comment in this article and I will answer you with a solution. If I don't know the answer, I can find someone who does.