Solution : https://service.sap.com/sap/support/notes/460434 (SAP Service marketplace login required)
Key words : 
symptom conntrans finishes successfully, basis support packages, troubleshooting option proposed, older qrfc version, solution - read note 0481278, starting conntrans, qrfc version 6, terms qrfc, data transfer, outbound queue
Related Notes : 
       
| 481278 | Installing qRFC Version 6.20.045 | 
| 442478 | Installation of qRFC Version 6.20.043 | 
| 438015 | Latest qRFC version and supplement for 3.x, 4.x, 6.10, 6.20 | 
| 400280 | OCS: Known problems with Support Pkgs in Basis Release 6.10 | 
| 173814 | OCS: Known problems with Support Packages for Release 4.6 |