The only time this happens to my knowledge is if the base (non-ISBoxer) Config.WTF file does not have an account name stored, AND your Virtual Config.WTF file for a character is newly-created (copied from that Config.WTF file).

To fix it... log into your team (at least to server/character selection) and check the Save account name box. It doesn't matter if it's the right one in the right window or not really, because if you get it wrong you can just close out the game windows, Export to Inner Space (at that point it will offer to fix the Config.WTF files, or you may even be able to Export without doing all of this...), and launch your team.