Have tested and retested what is causing this:
The addition of a textarea element to a HTML file.
File has previously been successfully previewed many times.
Tested adding the textarea with a combination (none, all, some) of the rows, cols and name attributes just in case it was expecting something that wasn't there: no difference. The inclusion of the textarea element causes Aptana to crash on preview attempt.
While I wasn't able to include a screenshot I did attach the various error logs I could assemble: aptana diagnostic, aptana log file (cleared then reproduced error) and system error report on crash (Mac OS X 10.6.8)
Aptana Studio 3 crashes about a second after pressing the preview button.
Expected successful preview/render.