[klippy]

It's an error because the Metamod developer deemed it so, even Sawce said that it's a harmless warning. That's not what crashes your server.
Taking a look at the code, I wouldn't even consider it a warning but an info message. It looks like Metamod prints it if it can't determine from which plugin a cvar or a server command comes from. It seems that info is only used for listing cvars and commands.