Hi Preetha,
Hope you are doing good.
Has the SSO ticket expired and is it loaded correctly. Refer the SAP note:1083421 and configure the SS0 settings again. Please run the SSO2 wizard and make the automatic connection to
the abap server. This will solve any inconsistencies on the server due to manual interventions.
Most likely reason for the error is that certificates were loaded manually to the ABAP server rather than using SSO wizard. More help:
<http://wiki.sdn.sap.com/wiki/display/EP/Troubleshooting+SSO+between+AS-ABAP+and+AS-JAVA>
Also the SSO enabling parameters should be set on the R/3 server. SSO Logon Ticket-> login/accept_sso2_ticket and login/create_sso2_ticket More info:
http://help.sap.com/saphelp_nw04/Helpdata/EN/22/41c43ac23cef2fe10000000a114084/frameset.htm
If the issue persists, go through SAP Note No. 1769367 - Issuer of SSO ticket is not authorized and the logs mentioned should help narrow down the case.
Thank you and have a nice day :).
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Kind Regards,
Hemanth