Did you install the Form Builder 2 HTML Editor Compatibility release? It should be a separate download on our web site in your download center.
You should be able to completely uninstall and remove Form Builder and HTML Editor... then install the Form Builder update with html editor 3 compatibility and then install HTML Editor 3.
Try following those steps and if you still have issues we'll open a support incident and have someone call you and debug this with you over the phone.