I think found the solution. Try doing this.
put debug mode to 0; empty the timthumb folder. refresh your page.
EDIT (moved from comments)
don't use px
, this :
$this->Fancybox->setPreviewContent($this->Timthumb->image('/img/gallery/' . $gallery_image['GalleryImage']['path'] , rray('width' => '267px', 'height' => '189px')));
should be :
$this->Fancybox->setPreviewContent($this->Timthumb->image('/img/gallery/' . gallery_image['GalleryImage']['path'] , array('width' => 267, 'height' => 189)));
UPDATE
Use the following lines on TimthumbController class
. It will work like a charm.
public function beforeFilter(){
$this->Auth->allow('image');
}//end of beforeFilter