Hi Anup,
We had similar issues when we were testing with SFDC Server for the first time.
We do not need any CA Certificates from Salesforce to resolve this issue.
It was resolved by adding below mentioned module configuration in SOAP adapter :
Module Name :sap.com/com.sap.aii.af.soapadapter/XISOAPAdapterBean
Module Key = soap
Parameter Name = trustStore
Parameter Value = TrustedCAs
Please refer to SAP note 1588148 as mentioned by Harish for more Info.
Regards,
Yeshwanth