i´m an old player,but didn´t logged on my account in ages,but these days i came back t the game and tried to play on the multiplayer mode and it didn´t work,always showing a message that occured an unxpected error and tells me to reload once i try to batle someone.

I suggest you clear your cache and game data and if necessary update to the latest version. If that does not help, send in a ticket to support.