This seems to be a bug that is introduced if you install Form Toolkit over Form Builder.
to fix this issue, please replace your current WAFV_Library_C.js file which is located under:
Configuration/Commands folder with the attached file.
Make sure to have dreamweaver closed and make sure to delete the cache file before restarting.
I have logged a bug in our bug base and the official fix should be included in the next dot release.