How to add multiple js files in hook_field_widget_form()?
Seems you missed step 3. from the README.


  
  Download the fancyBox plugin and extract the entire directory into    sites/all/libraries. (You may need to create this directory). The path
  to    fancyBox should be
  sites/all/libraries/fancybox/source/jquery.fancybox.js.    (the module
  uses the minified version, so actually jquery.fancybox.pack.js).
  


The second JS then doesn't fire anymore as the first JS virtually raised an exception already (due to the non-existent 3rd party library).