For setting up html extensions for IIS7, please go through the following procedure

 

1. Run IIS Manager .

 

2. Select your web.

 

3. Open handler mappings.

 

4. Click to Add managed handler... .

 

5. Set dialog values just as the following image shows.

 

 

Page url: http://devnet.kentico.com/docs/devguide/index.html?setting_up_html_extension_for_iis7.htm