Yanntastic

I have an error. When I try to open a shop with a currency other than #0 it crashes with this error message: "undefined method: '[]' for nil:NilClass. and it sends me to line 244 of the script saying "$game_party.currency[currency_index]". I input the exact script call as I was told before the shop processing so what am I doing wrong? Edit: I figured it out. The Shop Manager script I used was the error. I removed that script along with the shop stick script and now it's working just fine. Guess I need another way for adding a shop stock.