Check what Glawing pointed out, make sure the Battlin Bears have not already made a trade with the players involved. If the Bears traded the players to another team, then the trade offer with your team will be null and void.
If that is not the issue, send an email to firstname.lastname@example.org with all the details.
AFAIK that's the case after the release with each holding 168(?) manager spots. Biscuit atleast was full or "full" at some point so I guess it was necessary to add new worlds to keep the game growing when there were just 16*5 spots, like it is right now, per game world.
That is correct. When v2.0 is released, there will be one game world for each speed.