The error message- “Error In Message” in your Outlook Express (OE) is mostly because of your Internet Service Provider (ISP) and not because of OE.
You’ll, in most cases, be able to receive emails but will encounter “Error in Message” pop-up while you try to send or create new emails.
To solve this problem – call up your ISP (Internet Service Provider) and request them to reset your connection. Also ask them to issue new password, if you are required to authenticate before you access internet.
You may have to reset your modem too, for which you’ll have to unplug your modem from your computer / laptop and leave it uplugged for a while before you reconnect it.
Once you are done with these two, your Outlook Express should work fine.