You may find what you are looking for at http://www.codeconscious.com/outlook-express/backup-outlook-express.html
If all seems to fail you should be able to open the message folder that will not import or export, select all of it's contents (emails/messages) right click, copy then paste to a newly created folder on the other machines OE. Even if you must do this via a CD it should work.
Hope this is of some help.
System: AMD64, 2 gb ram, 200 gb hd, WinXp SP2, Outlook Express 6
I made backup copies of my Outlook Express folders to transfer them to another PC. I imported using File>Import>Messages>Microsoft Outlook Express 6>Import Mail from OE6 store directory. Most of the folders import without issue; some don't. Two folders that I renamed did not import, but another that I did not rename did not also. (They do not show as being available for Import.) I've tried this on 2 PCs with the same results. Does renaming affect the import process? Any suggestions?