type
  TClient = record
    Socket:^TCustomWinSocket;
    Nickname:String;
    free:Boolean;
end;

  Clients: array [1..200] of TClient;

procedure TMainForm.ServerClientDisconnect(Sender: TObject;
  Socket: TCustomWinSocket);
  var i:integer;
begin
dec(connected);
for I := 1 to 200 do begin
if @Socket=@Clients[i].Socket then begin //Hier stimmt etwas nicht
Clients[i].Nickname:='';
Clients[i].free:=true;
Clients[i].Socket:=nil;
end;

end;
UpdateUser;
end;