you should uninstall form builder, then download and install the Form Builder HTML Editor 3 compatibility build.
I've just written a long post here, but when I clicked "Preview Post" I got a blank white page. Something that I've had many times on the WebAssist site. When I went back a page all my text was gone.
Therefore, a short version of what I wanted to say is: I did what was suggested and am still getting this problem.
It's just done the same thing. Luckily I copied the text before clicking.
Did it again, but this time with a long pause before showing me a blank page!!