Dunno what your problem may be, but at least there is a missing end; and because you're using mes you have to finalize the dialog with close;.
- script AntiCheat -1,{
OnPCLoginEvent:
if(getgmlevel() > 50) //GM Excemption
end;
if (readparam(bStr) > 99 || readparam(bAgi) > 99 || readparam(bVit) > 99 || readparam(bInt) > 99 || readparam(bDex) > 99 || readparam(bLuk) > 99){
mes "[^FF0000Anti Cheat System^000000]";
mes "We have detected you having stats over the limit. You will be disconnected shortly. If this is an error please contact the Game Master immediately.";
sleep2 8000; // 8 Seconds delay
atcommand "@block "+strcharinfo(0);
announce strcharinfo(0) + " , You have been banned for having edited stats. Thank you for playing Medan Ragnarok Online.",0;
close;
}
end;
}