When loading a page using the HTMLAREA using IE6 on an all SSL enabled site, the default iframe source is about:blank. This produces a security warning about viewing mixed security content. The problem is that IE does not view about:blank as a secure source.

The fix is to change this file:
/lib/editor/htmlarea/lang/eng.php

Search for about:blank and point to to a blank page hosted on the moodle installation.