Hi Anil,
The first place to start is by reproducing the issue while running the troubleshooting wizard on the portal system (explained in note 1332726) here you can see if the login ticket was created ok.
Then on the backend you can check if the it recieved and accepted the ticket via an SM50 security trace. It should hopefully show the ticket recieved and give an error why SSO failed.
Httpwatch trace is also usfull to track the login ticket (MYSAPSSO2 cookie).
Also usual checks are to make sure the system are in the same domain and that the user exists on both systems.
Hope this help find the root problem.
Kind regards,
Cathal