I've noticed it does that if I attempt to search directories which require administrative privileges to access. So limiting your search only to your personal files folder (which I recommend be formatted as NTFS on an external drive so you can just grab it and go in an emergency, you can plug it into pretty much any other computer to access your files, and you don't lose your personal files when rolling back or reinstalling the OS) will prevent that. Further, clicking only the document types you want (at left in Catfish) will speed things up.