following error happened and I dont know why?

Hi the following error happened and I dont know why?

anyway of converting or anything

[DCC Error] MySQL.pas(2228): E2010 Incompatible types: 'AnsiChar' and 'Char'

function mysql_kill(mysql:PMysql;pid:longint):longint;
var buff:string[3];
begin
     buff[0]:=chr(pid AND $FF);//<-----------------ERROR-----------------
     buff[1]:=chr((pid shr 8) AND $FF);
     buff[2]:=chr((pid shr 16) AND $FF);
     buff[3]:=chr((pid shr 24) AND $FF);
     result:=simple_command(mysql,COM_PROCESS_KILL,@buff,4,false);
end;

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