2805155 - AS2 messages failing with error "Cannot write this object"

You have a B2B scenario configured in your PI/PO system and you can see some messages failing with the following error:

com.sap.engine.interfaces.messaging.api.exception.MessagingException: javax.resource.ResourceException: Message cannot be delivered: java.io.IOException: Cannot write this object. It has to be an instance of iaik.security.smime.JMailSMimeSigned or iaik.security.smime.SignedContent!  

• SAP Process Integration, connectivity add-on
• SAP Process Integration, business-to-business add-on

AS2, B2B, Addon, EDI, IAIK, BC, Message, Failed, JMailSMimeSigned, SignedContent, Process Integration 7.0, PI 7.0, PI 7.01, PI 7.02, Process Integration 7.10, PI 7.10, Process Integration 7.11, PI 7.11, Process Integration 7.30, PI 7.30, Process Integration 7.31, PI 7.31, Process Orchestration 7.4, PI 7.4, PO 7.4, Process Orchestration 7.5, PI 7.5, PO 7.5, XI, AEX , KBA , BC-XI-CON-B2B-AS2 , Applicability Statement Protocol Adapter , Problem