Form toolkit has not been updated for compatibly with DW CS6.
At this time, the only extensions we have that are compatible with DW CS6 are Design Extender, Data Bridge and eCart 5.
If you need to use Form Toolkit in DW CS6, I would strongly urge you to upgrade to data Bridge which includes form builder and other extensions. other wise, you will need to continue using your older Dreamweaver version.