Uploadify in laravel 4: HTTP Error 500

I get this error and i've been stuck trying to find out what i am missing to fix it.

Here is part of the form:

{{Form::open(array('action' => 'ProfileController@postUploadPicture2','files'=> true,'id'=>'uploadform2'))}}
{{ Form::file('file_upload',$attributes = array('id'=>'file_upload')) }}

Here is the uploadify part:

$('#file_upload').uploadify({
            'fileTypeDesc' : 'Image Files',
            'fileTypeExts' : '*.gif; *.jpg; *.png',
            'debug'        :'true',
            'swf'      : '../swf/uploadify.swf',
            'uploader' : url, //debe redireccionar al controlador
            'onFallback' : function() {
                                    alert('Flash player no detected.');
                                    },
            'method'   : 'post',
            'width'    : 150,//ancho del botón de browser
            'buttonText' : 'Choose your file...',
            'onUploadError' : function(file, errorCode, errorMsg, errorString) {
                                            alert(':-( The file ' + file.name + ' could not be sent. There was the following error: ' + errorString + ' Mensaje: '+ errorMsg + ' código: '+errorCode + ' File: '+ file);
                                            }

And Here is what i have so far of my controller which should return a simple message just for testing:

    public function postUploadPicture2(){
    return 'success';}

And the debbugging part:

SWF DEBUG: Event: fileDialogStart : Browsing files. Multi Select. Allowed file types: *.gif; *.jpg; *.png
SWF DEBUG: Select Handler: Received the files selected from the dialog. Processing the file list...
SWF DEBUG: Event: fileQueued : File ID: SWFUpload_0_0
SWF DEBUG: Event: fileDialogComplete : Finished processing selected files. Files selected: 1. Files Queued: 1
SWF DEBUG: StartUpload: First file in queue
SWF DEBUG: Event: uploadStart : File ID: SWFUpload_0_0
SWF DEBUG: ReturnUploadStart(): File accepted by startUpload event and readied for upload.  Starting upload to http://localhost/cimmgm/public/edit/upload_picture2 for File ID: SWFUpload_0_0
SWF DEBUG: Event: uploadProgress (OPEN): File ID: SWFUpload_0_0
SWF DEBUG: Event: uploadProgress: File ID: SWFUpload_0_0. Bytes: 39446. Total: 39446
SWF DEBUG: Event: uploadError: HTTP ERROR : File ID: SWFUpload_0_0. HTTP Status: 500.
SWF DEBUG: Event: uploadComplete : Upload cycle complete.
SWF DEBUG: Event: AssumeSuccess: 30 passed without server response

How can i fix this? what am i missing?

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