Try this first:
Then type "fatal error code 6" into the "Ask A Question" box at the top of the main Encore Forums page, or the top of the Discussions page.
You'll get 5 very relevant topics right away.
I did not realize until my tests a couple days ago that as of CS6, Encore deletes the authorsession folder upon completion of a build.
If it exists after a build, deletion is indicated, but users should be alerted that is they are CS6 and they don't find it, they should not worry.