there are two downloads the ADD-ON and the SDK, you want the ADD-ON, the ADD-ON will NOT have SDK in the file name, try installing and activating BLENDER4WEB ADD-ON if you get errors "clean up" previous attempts of installing BLEND4WEB ADD-ON in your blender add-on folder which is located in a hidden directory (Windows 7) AppData (C:\Users\%YOURWINDOWUSERNAME%\AppData\Roaming\Blender Foundation\Blender\2.73\scripts\addons) , I had to uninstall and reinstall BLENDER for the BLENDER4WEB ADD-ON to work, but I am a round peg and square hole guy and had a lot of baggage after 30 attempts of installation, great plug-in by smart people! Thank You