Because some functions from AMX Mod were moved into cstrike I think.
You shouldn't be compiling AMX Mod plugins directly. It'll work, and it's a quick way to port, but you shouldn't whine about bugs if you're doing it. You should put in the effort to at least change to AMX Mod X's native includes.
Let's just say we all don't dwell on this stuff 24/7 like some others and didn't know that. I mean to keep your server up-to-date is like a full time job now days. Thanks!