procedure TForm1.ServerSocket1ClientRead(Sender: TObject; Socket: TCustomWinSocket);

function IsInteger(s:string): boolean;
var i:integer;
begin
  {
    if not s[i] is a 0..9 then exit, else result is true :) }

  result:=false;
  for i:=0 to length(s) do
    if not (s[i] in ['1','2','3','4','5','6','7','8','9','0']) then
      exit;

  result:=true;
end;

var s: string;
begin
s := Socket.ReceiveText;
if s[1] = #36 then
begin
  if isinteger(s[2]+s[3]) then
  begin
    delete(s,1,pos(':',s));
    memo1.lines.add('Error:'+s);
  end else
  memo1.lines.add(s);
end;