If you open up a page in dreamweaver after installing it should run a secondary installer. Then after that runs you restart Dreamweaver one more time and it should have created that file and the error will go away.
If you have issues you can also reinstall the extension to start the process over and it should work. The steps are:
1) Close Dreamweaver
2) Install the extension
3) Open Dreamweaver
4) Open a new page and let the secondary installer run
5) Restart Dreamweaver