When CA Service Desk Manager (CA SDM) access types are configured to use "OS Authentication" and to allow external authentication, users can log in with their domain credentials. However, in large, multi-domain environments, some users may not be able to log into CA SDM with their domain credentials. The same thing can occur when using Embedded Entitlement Manager (EEM) for authentication in CA SDM, where EEM is configured to connect to multiple authentication domains.
CA Service Desk Manager 14.1
This problem could be caused by a user having non-unique accounts (meaning the same userid) on more than one domain in the environment. CA SDM and/or EEM does not know which domain to authenticate that user with as the username exists in more than one domain.
Work with network or domain administrator to locate the non-unique domain accounts and update them so that they are unique across the different domains.
User Authentication in CA Service Desk Manager