When Active Directory plugin is enabled on Ubuntu, and the user clicks on Manage Jenkins -> Configure, it results in the console staying at "Loading", or a page with this at the top:
Status Code: null
Exception:
Stacktrace:

(none)

Generated by Winstone Servlet Engine v0.9.10 at Mon Oct 17 03:29:59 CEST 2011

It may be necessary to have a windows slave configured to reproduce the error.

Edit: similar issue occurs with the slave-setup plugin as well.