Are you running the latest update of the Message Saver Pack? You should find in the README.TXT the most recent entry is 16 September 2004.
Which version of GroupWise is running where the error appears? Does the error appear for all kinds of message (Mail, Appointment, Task, Note, Phone Message) or only one?
It may help us resolve this error if you send the Formativ configuration for the user in question to firstname.lastname@example.org . You can obtain the configuration by selecting Help | About Formativ… from the GroupWise main menu. When the About Formativ dialog appears, go to the Configuration tab and click the button Copy to clipboard. Then paste the text into your email.
I look forward to hearing from you soon.