Im new to extjs and im trying to connect a form made by extjs to mysql database by a php file. the code i wrote looks fine to me i just cant see whats wrong, an error appears everytime i try to submit the form telling me Ext Error: you're trying to decode an invalid JSON string

<?
$conn = mysql_connect ("localhost", "root", "") or die (mysql_error ());
mysql_select_db ("extjs") or die (mysql_error ());
$q=mysql_query ("
INSERT INTO info (to, subject, msg) VALUES ('".$_POST['to']."','".$_POST['subject']."','".$_POST['msg'].`") or die; ('{"success": "false"}');//json output to notify the insert is success or not
if ($q) {
echo '{"success" : "true"}';
}
else {
echo '{"success" : "false"}';
}
?>`
can anyone tell me whats wrong? thank you.