Odd Error Message when Inserting File
 

When I insert a file into an outgoing email Outlook displays the error
message "could not open one or more attachments." In spite of that,
the file is attached to the email. There is no visible indication of
the attachment in the email as it is composed but the attachment is
shown when the email arrives and can be opened by its recipient. This
annoyance occurs with all file types and with both HTML and plain text
email styles. Any ideas before I uninstall/reinstall the entire Office
package?

Windows XP SP2, Outlook from Office 2000 Pro SP3.