Resolution :

enable "show hidden files" in the folder options, view tab.

Back up the email you wish to keep. (While rebuilding the mailstore shouldn't result in any loss of email, it is always better to be safe. )
Close Windows Mail.
Click the Start Button (Pearl) and select Computer.
Navigate to C:\Users\your username\appdata\Local\Microsoft\Windows Mail.
Delete WindowsMail.MSMessageStore.
Open the Backup directory.
Open the new directory.
Delete WindowsMail.MSMessageStore.
Open Windows Mail to rebuild the mailstore database.

You should now be able to view and delete the problematic message(s).