[PrO.GameR]

new Text3D:label = Create3DTextLabel("Admin On Duty!", 0xff387a,x,y,z, 40.0, 0, 0);
Delete3DTextLabel(label); //Delete 3d text label saying "Admin On Duty!"

You are recreating a new label, then deleting it !
Save it in a global variable like Jeff does (some aodlabel[playerid] or sth)