If you have the latest version of vBulletin Blog installed, you should be able to delete includes/blog_plugin_online.php. This occurs because of a conflict with old versions of the blog that used the file, but it is no longer used in newer versions. Because the file still exists on your server, it is being autoloaded by VaultWiki to be compatible with the early version.
If you are getting a Javascript error like this, you probably have to revert some of VaultWiki's templates.