IMAP folder cannot be deleted

When you try to delete an IMAP mail folder in Thunderbird, you may find that you cannot delete the folder and that you instead receive an error message that says "The current command did not succeed. The mail server responded: RENAME failed: Can't create mailbox [folder name]: File Exists."

In this case, try going to "Tools -> Account Settings -> Server Settings" and changing the option for "When I delete a message" to "Remove it immediately."