After upgrading DE 11.3 to 12.0.02, users with the group permission (below) are unable to open/edit users in Admin perspective under Admin -> Security, the error is "Unable to open Security. Ensure you have adequate security privileges."
ADMIN.SECURITY FILES.* Alter, Update, Read
CA Workload Automation DE r12.0.02
CA Workload Automation Desktop Client r12.0.02
The problem is at the Desktop client level where the security permissions that are sent did not match with the new security permissions level.
Assign the user group these security permissions;
ADMIN.Network Topology.* (Read)
This issue is fixed in Desktop Client 12.1 release.