[ikbenremco]

pawn Код:

if(issuerid != INVALID_PLAYER_ID)
{
    if(weaponid == 34)
    {    
        new Float:health;    
        GetPlayerHealth(playerid, health); //We're saving it to our new Float:health variable.    
        SetPlayerHealth(playerid, (health)-50);
    }
    return 1;
}

or replace
SetPlayerHealth(playerid, (health)-50);
with
SetPlayerHealth(playerid, -50);