The method is not working for you, but do you have the same problem? I mean, you have the no-permission error, but does the URL contain a valid contenttypeid value or not?
Check your wiki permissions and make sure that edits for registered users don't go into the moderation queue. Moderated users aren't allowed to post attachments. However, I think it's more likely that the content type ID is missing, since the permissions would be the same for the button and the popup as long as the ID is passed.
If the contenttypeid is missing, and you've tried clearing the cache, disabling/re-enabling VaultWiki, and the ID is still missing check your database's 'contenttype' table for a VaultArticle entry. Let me know if you find it or not. Also, please specify your exact vBulletin and VaultWiki versions. vBulletin changed the attachment code in almost every point release since 4.1.0, and introduced new problems that needed to be addressed with new VaultWiki patches. If you're using 4.1.6 or higher, we won't be able to help right now, since we don't have access to the source code for unreleased versions.