Blu-ray Error: "fatal error", Code: "6",
Note:"

I tried burning a Blu-ray in Encore CS3 and it worked once. Since then it spends
hours trancoding stuff when I go to burn and eventually just blows up with this
error (the subject of this message).

Happened to me a couple of times.
One solution was setting the button routing 'automatically'
In other words: no changing of the button routing before building.

Another time the issue was caused by a file which was transcoded but seemed to
cause the error.
I succeeded in finding the file, removed it, imported it again and let it
transcode.
This solved it for me.