I have a mirror back-up of my Outlook Express email, but when I try to open message folders I get an Adobe Reader 'can't open' message.
When I double-click on the zip folder containing the backups of my email (3_Outlook Express_Outlook ExpressIdentities_Main Identity_Email folders.zip) the foldericons have the Adobe logo. When I double-click on one of them Adobe Reader opens and then displays the message 'Adobe Reader could not open [dbx file name] because it is either not a supported file type or because the file has been damaged (for example it was sent as an email attachment and wasn't correctly decoded'. So I'm not choosing Adobe Reader, it's choosing itaelf! Does that help?