IDOCFlatToXmlConvertor for multiple idocs

Hi Experts,

Per the SAP Help documentation for PI 7.31 , IDOCFlatToXmlConvertor can be used to convert a FlatFile to an XML even if the flatfile contained multiple IDOCS. Initially, the partner was sending Flatfiles that contained single idocs and the scenario was working fine. When they send a Flat File containing multiple IDOCS we are getting the error :

Module Exception 'com.sap.aii.af.idoc.exception.IDOCModuleException: No data segments for DOCNUM

Has anyone encountered the same issue? The FlatFile looks to have a valid structure. We are using a sender FTP adapter to communicate with the sender system.

Thanks