Word error after a document attached to Outlook

[Erin]

After attaching a Word document to Outlook we receive the
following message when we open it from the un-sent e-mail:
"Word could not fire event"

There is nothing special about this Word document,
meaning, no tables, links etc..The receiver does not get
the error message, but when the sender opens the
attachemnt from her original e-mail she receives the
message. The obvious fix is not to open it from the
original e-mail, but we still want to know why this
happens.
Any info would be appreciated.
Erin