i know its a LLOOONNNNGGG time but I'm new to addon studio & i HAD the same problem & justfixed it :)
I did 2 things and not 100% sure which fixed it but its fixed :D
1) u need a key named "GamePath" in the registry in "HKEY_LOCAL_MACHINE\SOFTWARE\Blizzard Entertainment\World of Warcraft" having the installation folder of the game
2) run the game in administrator mode (as the GMs say) that should make WoW automatically add required registy keys.
reinstall add-on studio should get u up and running
NOTE: i also had a problem where all the frames were kinda empty (just a rectangle) that fixed it too, when u run the add-on the game should start
I hope this helps u or any1 who stumbles upon the same problem :)