Looks like you are using a script from ORTS/server, they use a seperate file for storages.
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It tries to index global 'Storage' (a nil value), there is nothing that defines what Storage is in your NPC script, either add a file like I linked above or rewrite it to a storage value instead.
Lua:
player:getStorageValue(number)
player:setStorageValue(number, value)