I see the problems here:
1. when I set Preferences -> General > On startup -> Do not open anything and start WeBuilder, I have HTML and CSS toolbars enable. So click W3C CSS Validator button -> WeBuilder bombs with AV and falls into the loop. I have to kill it with Task Manager. BTW there is no hint for W3C CSS Validator button.
2. In Preferences -> Choose Editor Font -> Font Style is empty. For me should be the last selected i.e. Regular.
3. CSS Preview doesn't recognize:
DIV#Footer {
font-size: 7pt;
font-style: italic;
text-align: center;
margin-top: 0.2cm;
margin-bottom: 0.2cm
}
I checked the problem is with "#".