Hmm strange! How did you install the extension? Sounds like you might have tried placing in script folder but it is actually just a mater of double clicking on the extension file :)
See the installing part in the video below! Let me know if this works or not! (Skip to 40 secs in if it doesnt automaticly)
Alternatively you can also navigate to Edit>Preferences>Extensions and press add extension then navating to where tou downloaded the tool :)
Again let me know if this helps! :D