Apple Configurator: The spreadsheet provided has redemption codes for "(null)."
I'm trying to import a spreadsheet of redemption codes into Apple Configurator. I download the spreadsheet directly from https://vpp.itunes.apple.com, but when I try to import it, I get the following message:
Apple Configurator: The spreadsheet provided has redemption codes for "(null)."
What can I do to import it?
iPhone 4, OS X Mountain Lion (10.8.2)