First, can I suggest you ask this in a Groupwise support group (as well) if
you have not already done so - someone else was asking in here about
Groupwise recently and much as we would like to help, I don't think any of
the regular participants has a Groupwise set-up available for experiments.
furthermore I think she could have used some help on how to make Groupwise
work with merge.

Curiously, this message is so old it does not actually have anything to do
with Exchange /Server/ (as far as I know) but refers to the Microsoft e-mail
client called "Exchange" that eventually turned into the full Outlook. First
I would check that your user has the same default e-mail client set up as
everyone else - if you are using IE you can look in IE|Tools|Internet
options|Programs. But the chances are that the message is to do with MAPI
settings, possibly
a. the version of MAPI32.DLL (probably in Windows\System32) could be
different
b. the [Mail] settings in Windows\win.ini might be different, or the
equivalent registry settings which are I think stored in the registry at
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows Messaging Subsystem]

It might also be worth checking to ensure she has not had updates to Windows
or Office (or the Groupwise software) that have not been installed for
others, and that she has not inadvertently done something like tried to
modify the MAPI services in her profile (not sure how you do that if you
don't have Outlook etc., but perhaps there is a way).

Sorry to be vague...if you do find the cause/solution please post back, or
if that sparks some ideas I can try to think of other possibilities.

Peter Jamieson