People with this problem, often need to delete multiple messages or entire folders. That error appears because WLM only thinks it has that/those message(s), but actually that message is nowhere to be found in the Windows email folders. The message exists no longer, but WLM still shows it being in its own folders and you simply cannot delete it using the normal procedure.
Indeed, one can drag the unwanted and non-existing emails to the Deleted Items folder, one by one. However, that is crazy when you have to get rid of hundreds or thousands of them (yes, I had that situation!).
This is how to trick WLM if you want to delete multiple emails giving you that error:
1. We try to simulate forwarding multiple messages. Select multiple emails by clicking on one and then using SHIFT to click and select multiple concatenated messages. Do that screen after screen (scroll down/up). Stop when you see the FORWARD button becoming grey. That means one email is even more stubborn.
2. Hold the SHIFT key and click the messages up and down until you find the culprit. It will be just outside your selection, when your selection manages to un-grey the Forward button.
3. With a lot of messages selected and concatenated, click on the Forward button. You'll get an error message "One or more messages could not be attached. Select OK to continue creating the note." Click Cancel.
4. Now something has unblocked those messages and, with the selection on, you can Delete them by simply clicking the Red X (delete) button.
5. The message that made the Forward button grey, can be deleted as well.
6. Keep doing that until you finish the bunch of messaged you wanted to delete, when you got the initial error.
