Messenger Error: MailMsgAtt not available

I have a Word document that has imbedded outlook emails.
When I attempt to open certain of the emails, I receive
an error message stating

This message was created in MailMsgAtt. This application
is not available to open this object. Make sure the
application is properly installed and that it has not
been deleted, moved or renamed.

I can find no reference to the application MailMsgAtt on
the Microsoft website and need your insights/thoughts.

Thanks in advance.