Hi Sree,
1. There might be a mandatory field in contact person in ECC which is not filled.
2. If the direction of the replication is from CRM to ERP and you have not filled any of the name fields for contact person here in CRM, this error might occur. Because in ERP system the last name field may mandatory.
So you need to fill the Name fields here and check the Bdoc monitor through smw01
Hope this will help
Thanks and Regards
DJ