howcome when i use invitation on the knight.. it works.. but when i try it and goblins or chocobos.. it doesnt work.. it keeps saying guarded..

i tryed it on the bone headed guys too.. the ones that do thunder soul .. it keeps saying guarded


when i read the invitation skill.. it said somethin about

-Invites "Non-Human" monsters to party-


does the invitation skill not work on goblins or chocobos or wat?