|azjeffb, I'm assuming that the attachment has a .eml file extension. If it does follow the instructions under "To run the Msimn executable file with the /reg option" at the link below.|
OLEXP: Unable to Open EML File Attachments in Outlook Express.
If that doesn't correct the problem click Start>Run and copy & paste or type in (including the quotation marks).
"C:\Program Files\Outlook Express\msimn.exe" /reg
Note that the spacing is important so a copy & paste is the way to go.
I'm assuming tha C: is the letter of the hard drive that Outlook Express is installed.