Uploadify onComplete not firing

I am using Yii framework with uploadify. The upload works perfectly but the onComplete event gets not fired..

It seems that the main problem of most of the users is that the .php file does not return anything and so flash does not know when the .php script has finished. But my script does echo "OK" at the end, so this is not the problem.

My Code:

$('#element').uploadify({
    'uploader开发者_StackOverflow中文版' : 'index.php?page=upload',
    'swf'      : 'javascript/uploadify.swf',
    onComplete : function(event, queueID, fileObj, response, data) {
        alert(event); alert(queueID); alert(fileObj); alert(response); alert(data);
    },
});

My PHP Code looks like:

//Upload things
echo 'OK';

The upload works perfectly, but the onComplete event is not fired. I tried to remove all upload things, so that the php file looks like:

echo 'OK';

but that also does not work.

Thanks for your help!