OK!
I have solved the problem.
It seems due to the part of NOW();
require_once("connectdb.php");
if(isset($_GET["name"])!=""){
$query_insert = "INSERT INTO `1100108128`.`MB` (`ID`,`USER`,`TITLE`,`MESSAGE`,`TIME`,`EMAIL`) VALUES (";
$query_insert .= "NULL,";
$query_insert .= "'".$_GET["name"]."',";
$query_insert .= "'".$_GET["title"]."',";
$query_insert .= "'".$_GET["message"]."',";
$query_insert .= "'" . date('Y-m-d') . "',";
$query_insert .= "'".$_GET["email"]."');";
if(!mysql_query($query_insert))
die ("Invalid query");
header("Location:Messageboard.php");
}
?>