First - Make sure the Address fields and country state codes were uploaded correctly for your Accounts.

The Address field must contain the street address (not a building name or other location name), the country must be loaded as the official 2 letter country code, the state is up to a 3 letter state code. 

Also good to know - when you upload an accounts file, it wipes out all the agent IDs associated with the Accounts, so make sure you keep the column that associates Accounts to sales reps each time you upload an Accounts file.