You have this message when the control center service is enable to start an ABAP report.
By checking the Warehouse Builder Control Center Service log file, you will see this error :
2009/03/20-15:40:03-CET [11D3226] java.lang.NoClassDefFoundError: com/sap/mw/jco/JCO$Client
at oracle.wh.runtime.platform.operator.sap.NativeSAPOperator.execute(NativeSAPOperator.java:195)
at oracle.wh.runtime.platform.adapter.rtp.NativeExecutionAdapter.execute(NativeExecutionAdapter.java:43)
at oracle.wh.runtime.platform.service.controller.ExecutionController.execute(ExecutionController.java:70)
at oracle.wh.runtime.platform.service.controller.ExecutionController.execute(ExecutionController.java:23)
at oracle.wh.runtime.platform.service.ExecutionManager.run(ExecutionManager.java:36)
at java.lang.Thread.run(Thread.java:534)
This error said that the OWB - Control Center Service isn't able to find the class com/sap/mw/jco/JCOClient.
This class belong to the SAP JCO connector.
If you work with Warehouse Builder 10.2, you must install the version JCO 2.18.