I installed 1.5.3 version on vBulletin 4.2.0 (Patch 2). Everything works OK, the sidebar shows as it should, but I noticed that pages load really slow. When I disable the plugin it returns to normal.
I used PageSpeed insight from google to see what is going on, and when the plugin is enabled there are two redirects being triggered when I load the forum page:
http://[forum name]/install.php?reason=invalid_vb_dir
My sidebar contains only static images.