This error occurs when using the 3rd script generator option as selected at Admin -> Spaces -> Settings -> Community Everywhere:
Display "Discuss This" Link, Recent Posts, and Comment Box (aka /everywhere/780)
The first two options (777, 778) work fine and offer a "Discuss This" link when no comments have been posted yet.
If I embed the script as a 777 or 778 and create a comment thread first, then I can change the script to point to 780 and it works fine including showing the comment box. The error only appears if a comment thread does not exist yet.
I'm guessing you (Jive) know what I mean about 777/778/780 but just let me know if you don't.