Thanks for reporting this problem.
Which version of Message Viewer are you using? The current release (2.0.2) prints the recipient email address if the display name is blank. In rare cases (when the original GroupWise message has been corrupted), both display name and email address are blank; if so, the Viewer prints ‘Not available’.
You can download the Viewer (a free product) from:
Please let me know how you go.