Please upgrade to 2.2 here.
The 2.0 and 2.1 branches are no longer being updated.
Possible bug? Deleting discussions in embedded vanilla
Upon deletion, the page redirects to /vanilla/discussions regardless of where your forum is, so if it isnt in a subdirectory of /vanilla, it 404's.
The redirect is on Line 542 in applications/vanilla/controllers/class.discussioncontroller.php