My problem has been resolved! I had the "Send Stored Codes" box checked under the mistaken notion that I needed it checked in order to use my discount codes.
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I've got four ebooks for sale. I'm receiving emails that the inventory is out of stock. When I go to Inventory Control, I cannot uncheck "limit available stock". It is "grayed out". I've tried entering into the Item Expiration box for a date way in the future and tried leaving it blank. Neither allows me to still uncheck "limit available stock". Is there some other method I am missing? Thanks!