Solution : https://service.sap.com/sap/support/notes/1336383 (SAP Service marketplace login required)
Key words : 
send serialization messages, serdat idocs remain, note assistant orimport, relevant support package, terms report rbdser03, report rbdser03, partner profiles, outbound processing, bd42 reason, required decoupling
Related Notes : 
       
| 150202 | ALE: IDoc outbound - IDocs remain in status 30 |