The XNAT 1.7.4.1 release is a hotfix release that fixes a small number of urgent bugs that exist in the XNAT 1.7.4 release.
You can view the full list of issues that are addressed in the 1.7.4 and 1.7.4.1 releases here: https://issues.xnat.org/secure/Dashboard.jspa?selectPageId=12000