Malformed message ID: Line 3 References too long

This error message occurs when you reply to a deep thread in newsgroups. Line 3 is the References header. It contains the message ID of every message in the thread. When this line becomes too long, Outlook Express adds a carriage return instead of removing some of the IDs in the middle. This makes the last message ID invalid and so your reply is blocked from being sent.
Important Update
This workaround relies upon an *.eml file on your disk that includes the X-UNSENT: 1 header. If you install Security Update KB911567 this header is disabled for all saved *.eml files. To use this workaround you must first uninstall this update. Read more..
To work around this bug, save your reply to your desktop by clicking Save as on the File menu. Open the saved *.eml file in Notepad and edit line 3, References, by removing some of the message IDs in the middle. Be sure to leave the first and last IDs so that your reply will thread properly once it is posted. Saved your edited file, then double-click it to open and click Send.
An alternate method is to save, not your reply, but the message to which you want to reply. Edit the saved message to remove some of the message IDs, save the changes, then open the edited file and click Reply.