[SyS]

You might want to change the

PHP Code:

SendClientMessageToAll(DUEL, string); 


or add break in that last if condition

PHP Code:

if(DuelCountdown == 0)
{
/*your code*/
   break;
} 


It sends to all players and the loop still iterates for other players in duel too as no break in iteration is provided and therefore, it repeats the message.