Yes, that seems to have fixed it, although the path for me was:
I didn't have to go into the en_US folder.
What I did find though was that there was only 35 items in the attached download, but there is 46 items in the existing Forms folder. There was only three files that seemed to be missing, one is the formInsert.js which is causing the problem, and the others are Jump Menu.htm and Jump Menu.png
This leads me to believe that there are three possible causes for this:
1. Installing extensions regardless of vendor deletes these files;
2. Adobe forgot to add them back into the folder when their team was working on an update;
3. Adobe have changed the code or files it is using to insert forms which has greater implications for extensions installed!!
I hope it's number 2, but I bet it's number 3 :(
I say this because I have removed the file and tried inserting a standard form from DW, and it worked!