Cannot load into the Country lookup in addresses

Hi,

I performed a test load of 30 records into the Account addresses object, the first 30 records were imported but when attempting to re-import those records, the wizard returns this error: 

Column CountryName value cannot be obtained because it has not been loaded.

When i checked the values in the Country lookup, the values its rejecting are already loaded in the lookup, so it doesn't make sense that its saying its not loaded. There maybe something i'm missing here and i would love to know if anyone has experienced this issue in the past. 

Thanks!