Your target system JAVSYS seems to be some Java application with running JCo 3.0 standalone plus the Java IDoc Class Library 3.0 Add-On.
The full (non-truncated) error message is most likely this error message:
"The JCoServerFunctionHandlerFactory com.sap.conn.idoc.jco.rt.DefaultJCoIDocCallHandlerFactory returns null for function name <RFM_NAME>"
So this issue needs to be examined at the external Java side.There is either some JCo configuration error with missing RFC or IDoc meta data or you are sending usual RFC calls to a Java target system that is supposed to handle IDocs only.
Best regards,
Stefan