OAM 11.1.2.2 (11gR2) - System error after submitting credentials from Custom Login Page

Scenario : Standard Custom Login Page doing form post to /oam/server/auth_cred_submit with username/pwd and 'request_id' in cookie.

Issue - Sporadic redirection to an error page with 'System Error has occurred' message with details -

[oam_server1] [TRACE] [] [oracle.oam.binding] [tid: [ACTIVE].ExecuteThread: '3' for queue: 'weblogic.kernel.Default (self-tuning)'] [userId: ] [ecid: 004sto37QpzDoYX5HvH7if00063I00002b,0:2] [SRC_CLASS: oracle.security.am.pbl.protocol.plugin.oam.AMFailureResponseHandler] [APP: oam_server#11.1.2.0.0] [SRC_METHOD: processResponse] [URI: /oam/server/auth_cred_submit] OAM-02073[[

oracle.security.am.common.utilities.exception.AmRuntimeException: OAM-02073
at oracle.security.am.engines.enginecontroller.AuthzEngineController.checkProtected(AuthzEngineController.java:438)
at oracle.security.am.engines.enginecontroller.AuthzEngineController.processEvent(AuthzEngineController.java:177)
at oracle.security.am.controller.MasterController.processEvent(MasterController.java:570)
at oracle.security.am.controller.MasterController.processRequest(MasterController.java:759)

Solution - 

As per Support Document Id 1578776.1-

"Verify that the custom login page is submitting the credentials to /oam/server/auth_cred_submit with the correct OAM Server Host and Port.The OAM_SERVER_HOST.DOMAIN and SSLPORT values should match those configured in the OAM Console -> System Configuration -> Access Manager Settings page for Load Balancing OAM Server Host and OAM Server Port.”

In  my case, the form post URL was pointing to https://<host>/oam/server/auth_cred_submit.

Once I had it changed to https://<host>:443/oam/server/auth_cred_submit, (adding missing port) this issue got resolved.

Please check the above support document for some other causes for this issue.