If you are unable to login to the Unified Management Portal (UMP) and the following are true:
You are running into a limitation with liferay, a technology that UMP is built on. The "nimbus" user that you are creating must be in lowercase for it to login to UMP.
This issue does not exist with LDAP users due to a different authentication path.
Please only use alphanumeric lowercase characters for administrative "nimbus" users. These are users who are able to login to Infrastructure Manager, Admin Console and UMP. They are able to view all origins unlike account contacts are created within the Infrastructure Manager or Admin Console instances.