I tried to logon to two different SAP systems. I use JCo and succeeded in logging on to the productive system. But when I tried to log on to the development system, I received the error "com.sap.mw.jco.JCO$Exception: (103) RFC_ERROR_LOGON_FAILURE:". Both systems are in another network. Any suggestions? I suspect the security problems like RFC port error. Is it possible to get this error message if the RFC Port is fire walled?
I would have liked to see the detailed message that comes back with the RFC_ERROR_LOGON_FAILURE, so I have to guess here: If there really is a firewall issue, as you are probably correct in suspecting, then you have to use SAP Router to tunnel the firewall. SAP Note 30289 has useful information about the deployment of said product.
This was first published in January 2003