Solution : https://service.sap.com/sap/support/notes/1178628 (SAP Service marketplace login required)
Key words : 
xx-ser-net-htl reason, current customer problem requires, transaction sm51 -> instance list, customer problem occurred, support team accesses, sap support portal, internal error location, correct instance numbers, error message, saprouter instance
Related Notes : 
       
| 962516 | Solution Manager Services | 
| 812732 | R/3 Support service connection | 
| 707848 | SAPinst GUI service connection on SAPNet R/3 Frontend | 
| 701588 | Setting up Service Citrix MetaFrame connection | 
| 605795 | Windows Terminal Server connection in remote support | 
| 592085 | Installing HTTP Connect service | 
| 545519 | Java remote debugging | 
| 508140 | Customer messages - Customer logon data | 
| 356635 | T.120 Setting up a NetMeeting connection | 
| 202344 | Setting up SAP DB connection | 
| 195715 | Service connection types "BW RFC" and "BW GUI" | 
| 125971 | Service connection Upgrade Assist. in SAPNet - R/3 front end | 
| 100740 | Setting up a PCanywhere connection in the SAP Support Portal | 
| 79411 | AS/400: 5250 connection to AS/400 customers | 
| 37001 | Telnet link to customer systems | 
| 35010 | Service connections: Composite note (overview) | 
| 31515 | Service connections | 
| 30289 | SAProuter documentation |