ORA-12631 using Database Links with Oracle DBMS 19c on Windows Server 2019 We had a set of long-time Oracle 12c Database installations (multiple instances on separate VMs) on Windows Server.  Over the past year we transitioned to Oracle 19c on Windows Server 2019.  We found that database links that worked in the 12c environment did not work in the 19c environment; a query referencing such a link would fail with the error ORA-12631: Username retrieval failed.  SQLNET traces showed
naun5validate: SPP is NEGOTIATE 

naun5validate: SSPI: 0x8009030c error in AcceptSecurityContext
For many years we have adjusted the configuration of our Windows DBMS hosts by revoking the Access this computer from the Network User Right from the Everyone group.  With previous versions of Oracle DBMS this did not cause an issue, but with 19C we found that we needed to grant this user right on each database link target host to the AD service account used to run each database link source host.