I suspect you have come across a somewhat obscure bug in GroupWise another user reported recently. It appears that a particular sequence of HTML involving the Marquee tag can cause the GroupWise spell checker to throw an access violation. It does depend on the layout of the HTML. This is nothing to do with Formativ. You could test this by composing a new HTML message, then pressing F11 and retrieve the HTML signature file into the message. Once retrieved, spell checking the message should cause the AV to occur.
Novell were able to duplicate it and allocated it defect no: 414866 against the GroupWise 6.5.5 client. They reportedly fixed it in GroupWise 7.
The only workaround is to remove the marquee tag from the HTML (which is a shame, because that’s what causes the night scrolling effect), or spend the time playing with the HTML to try to find a combination that doesn’t cause the problem.