XNAT 1.8.4.1 is a hotfix release, addressing an issue identified by the XNAT community that can block elements of the Admin UI and Administer Users UI. This issue only affects installations of XNAT 1.8.4 – we strongly urge all installations to upgrade to this version.
See Documentation: XNAT 1.8.4.1 Release Notes
For older versions of XNAT, upgrading to XNAT 1.8.4.1 also includes all the benefits of XNAT 1.8.4.
See News: XNAT 1.8.4 Released