Ok, I've figured out the problem. Some ZIPs translate into nearby ZIPs when doing location targeting. For example, if you enter 85285, which is a ZIP in Tempe, AZ, AdWords will change it to 85281, which is also in Tempe, AZ. These locations are about
four miles apart though.
So if I have both 85285 and 85281 on the CSv which I'm uploading, it will show as 85281 twice, and neither will upload. I'm fine with only having one, because I can't imagine the four miles will make that much of a difference, but how can I circumvent this problem?