jQuery load() form serialize

i've got a problem with the load Methode from jQuery. Here my code:

$('#form').submit(function( event ) {
    $('.response').load('responseData.php?'+
                                     $('#form').serialize());
    event.preventDefault();
});

<form id="form">
        <input type="text" name="title" id="title" />
        <input type="text" name="text" id="text" /><br>
        <input type="submit" value="Speichern" class="submit"/>
</form>

<div class="response"></div>

The file responseData.php exists. But when I click submit, i get an '500 internal error'. The path is correct it is: http://ift.tt/1bGsJ7k

Do you know what's going on here? I'm really desperated.

Thank you!