Sagar,
In his words, he had missed the API login permission in the role setup.
In case you do not have them, I found these resources below very helpful. They describe the steps for the API setup.
http://help.sap.com/cloud4hr - go to product APIS,
next to SF API's Programmers Guide -
http://help.sap.com/saphelp_cloud4hr/helpdata/en/86/2e8238648a4529abda8f2b8a7fdd3c/frameset.htm
API handbook -
http://help.sap.com/saphelpiis_cloud4hr/en/successfactors_hcm_suite_sfapi_handbook_en.pdf
Robin