Hey there Ken,
Having just spent the last hour on the phone to MS Tech Support I have found
out what is happening here (it was happening to me too)
If you are trying to send a file, and the office application that created
that file is still open then you will receive this error. Try saving the file
and then closing MS Word, when I send the file now it works fine & dandy.
So to roundup if the file is still open in MS Word, Access, Powerpoint or
Excel it will not allow you to email it over.
Paul