[JaTochNietDan]

Your coding syntax is a little strange. Those brackets for example after the else if check do absolutely nothing except make it look pretty, they aren't part of any statement. Here is how I would code it:

pawn Code:

dcmd_setplayerhealth(playerid, params[])
{
    new targetid, Float:amount;

    if(sscanf(params, "uf", targetid, amount)) return SendClientMessage(playerid, 0xFF0000AA, "Usage: \"/setplayerhealth <playerid> <amount>\"");
    if(targetid == INVALID_PLAYER_ID) return SendClientMessage(playerid, 0xFF0000AA, "Player not found");
    if(amount > 1 && amount < 101)
    {
        new playername[MAX_PLAYER_NAME], targetname[MAX_PLAYER_NAME], string[256];
        GetPlayerName(playerid, playername, sizeof(playername));
        GetPlayerName(targetid, targetname, sizeof(targetname));

        format(string, sizeof(string), "%s(%d) set %s(%d)'s health to %.0f", targetname, targetid, playername, playerid, amount);
        SendClientMessageToAll(0x50FF05FF, string);

        SetPlayerHealth(playerid, amount);
    } 
    else SendClientMessage(playerid, 0xFFFFFFFF,"Error: Please use |Max|: 100, |Min|: 1");
    return 1;
}