ID:178246
 
Unrecognized or inaccessible verb: say

How would i make it instead of saying that, say this: "Unknown command"

like making custom error messages?
I don't think you can.
In response to Nadrew
awwww
In response to ShadowSiientx
Wait. I got it:

client/Command()
if(!mob.verbs.Find(src))
mob << "Invalid command"
In response to Nadrew
Hehe, thanks nadrew.