grunt concat issues

Hi, nice work you did here! I'm having a strange issue when running concat task with my Gruntfile.js

Running "concat:generated" (concat) task
Warning: Unable to write ".tmp\js\storyjs-embed-cdn.js?v214" file (Error code: ENOENT). Used --force, continuing.

As a result the js concat process produces 0 files and uglifyjs does not work. Any clues?

Thanx!
