I think the uploader is expecting your RobotPlayer.java to be in a top-level package, so you cant nest teams below a top-level package.
However, you can have multiple top-level packages.
If you have
Robot2.RobotPlayer.java then it should still work fine, as long as no files from
Robot1 package try to reference/import any files in
Robot2 package. You can tell the uploader which team you want to use at upload time, it will ask you which package to use, just tell it
Robot2 (Or whatever your actual package names are).
Also, just for reference, package names aren't limited to team name or number anymore. It can be whatever you want.