php - I am getting error "Undefined Index msg" above my form. All works Great the form too. But why am i getting the msg above the form.

This is the line of code that i used on my contact.php.
And

if(mail($to,$subject,$message,$headers))
    header("Location:../contact.php?msg=Successful Submission! Thank You for Contacting us.");
else
    header("Location:../contact.php?msg=Error To send Email !");

I just see the 'msg' in this code what can be done?