I ran into a similar issue using a custom implementation of RWD, so it might help to look this over:
Configurable product image not switching with swatch change
The main issue was tracking down the correct files that needed to be loaded on the front end for the JS to work. Taking a look there would be where i would start.
After that i would check the file permission, as they can seemingly get out of wack depending on changes that might have been made to the server, file system or install of some extensions ect......Take a look to see if there are any 404 errors in the developer console of your browser, as the files you are trying to switch to might not be found.