How to change the skin of a model when spawning from menu

Ok so I am making a SNPC and it’s for star wars, the clone models, but for whatever reason when I use this code

 self:SetSkin( 1 ) 

and that makes the model a ERROR in game, although I know there is more than one skin. In game you can change the skin easily by right clicking and the skin drop down but for whatever reason that code I use within the init for the NPC makes the model a error if it goes past 0.

That function could NEVER make the MODEL an error. You are setting incorrect path to your model most likely.