It is an automatic system that kicks you after an hour passes without selecting a country. Did you have some sort of issue selecting your team or country?
Now that you have gotten that message you should be clear to join that game again, you just need to continue through the selection process.
Currently there can be a little hitch in team games with country selection is enabled. If you join a team that already has one more player than another team you will not be able to select your country and will have to "skip and choose randomly"
For example if there are two teams, blue team has 2 players and red team has one player: If you select the blue team that would make it 3 to 1. If you try to select your country you will get an error message that states "this country has already been chosen" and you will get that message for all of the potential countries. It is a balance feature so that you can't stack your team with the best countries before other players join. When you get that message you will have to skip and choose randomly, or wait for someone to join the other team and balance things.
