3304949 - Bean RSRD_X_PRODUCE_PROXY not found on host "XXX"

When using SAP Portal to connect to the backend system with JCo, the connection fails and the following error appears in the  dev_jrfc.trc trace.

Exception thrown []:Exception thrown by application running in JCo Server
java.lang.RuntimeException: Bean RSRD_X_PRODUCE_PROXY not found on host "XXXX", ProgId=XXXXXX : Object not found in lookup of RSRD_X_PRODUCE_PROXY.
    at com.sap.engine.services.rfcengine.RFCDefaultRequestHandler.handleRequest(RFCDefaultRequestHandler.java:138)
    at com.sap.engine.services.rfcengine.RFCJCOServer$J2EEApplicationRunnable.run(RFCJCOServer.java:211)
    at com.sap.engine.core.thread.impl3.ActionObject.run(ActionObject.java:37)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sap.engine.core.thread.impl3.SingleThread.execute(SingleThread.java:185)
    at com.sap.engine.core.thread.impl3.SingleThread.run(SingleThread.java:302)
Caused by: com.sap.engine.services.jndi.persistent.exceptions720.NameNotFoundException: Object not found in lookup of RSRD_X_PRODUCE_PROXY.
    at com.sap.engine.services.jndi.implserver.ServerContextImpl.lookup(ServerContextImpl.java:653)
    at com.sap.engine.services.jndi.implclient.ClientContext.lookup(ClientContext.java:430)
    at com.sap.engine.services.jndi.implclient.ClientContext.lookup(ClientContext.java:714)
    at javax.naming.InitialContext.lookup(InitialContext.java:417)
    at javax.naming.InitialContext.lookup(InitialContext.java:417)
    at com.sap.engine.services.rfcengine.RFCDefaultRequestHandler.handleRequest(RFCDefaultRequestHandler.java:117)
    ... 5 more

SAP Portal 7.5.

broadcast,  RSRD_X_PRODUCE_PROXY, Bean not found, Object not found in lookup of RSRD_X_PRODUCE_PROXY, RSWR_SYSTEM_ALIAS_CHECK_PROXY , KBA , BC-MID-CON-JCO , Java-Connector , Problem