One user can't open 8bit encoded attachments

[NoJags Neil]

In other words, she *can* open:
------=_20040113181659_96122
Content-Type: application/octet-stream;
name="test.rtf"
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
filename="test.rtf"

but *can't* open:
------=_20040113181659_96122
Content-Type: text/richtext;
name="POPR Report.rtf"
Content-Transfer-Encoding: 8bit
Content-Disposition: attachment;
filename="test.rtf"

The latter *can* be opened on the intranet with OWA, but trying to open it
in Outlook 2002 produces the error attached.

Any ideas, causes, fixes?