Hello Jörg,
in this case please check your settings in ECC gateway.
Is your reginfo.dat maybe restricted?
Please check your Gateway security for Registered Programs via transaction = SMGW, menu = Goto -> Expert Functions -> External Security -> Display (Reg. Info).
There are some SAPNote which could help you:
http://service.sap.com/sap/support/notes/1069911
1444282 - gw/reg_no_conn_info Einstellungen
Best regards
Bastian