Hi All,
I have solved this error with the help of Sreenivas's reply. Yes, I created a SI which had a different namespace.
For receiver IDOC, we can just drag and drop the IDOC for SI in Operational Mapping. Even if we create a SI, we have to make sure that, the namespace is,
urn:sap-com:document:sap:idoc:messages
This namespace is a constant for all receiver IDOCs.
I later faced an error
com.sap.aii.af.idoc.exception.IDOCAdapterException: Recipient Partner Type is not available
Since I was just developing a scenario for learning purpose, I did not map all the fields. I just mapped the mandatory fields in the EDIDC40 segment. Even though RCVPRT ( Receiver Partner Type ) is not mandatory, it would result in error if we don't map it.
Thanks a lot Sreenivas.