"Empty test plan" when trying to merge

Hi,

I'm having a problem when I try to merge a .jmx file into my test plan, via
JMeter interface: it appears the following error message: "Empty test plan -
see log file". The log file is the following:

2014/06/27 19:19:16 INFO - jmeter.gui.action.Load: Merging file:
/home/higo/Downloads/apache-jmeter-2.11/shibb.jmx
2014/06/27 19:19:16 ERROR - jmeter.save.SaveService: Conversion error
com.thoughtworks.xstream.converters.ConversionException: null : null
---- Debugging information ----
cause-exception : java.lang.NullPointerException
cause-message : null
class : org.apache.jmeter.testelement.WorkBench
required-type : org.apache.jmeter.testelement.WorkBench
converter-type : org.apache.jmeter.save.converters.TestElementConverter
path :
/jmeterTestPlan/hashTree/org.apache.jmeter.testelement.WorkBench
line number : 3
class[1] : org.apache.jorphan.collections.ListedHashTree
converter-type[1] : org.apache.jmeter.save.converters.HashTreeConverter
------------------------------- : null : null
---- Debugging information ----
cause-exception : java.lang.NullPointerException
cause-message : null
class : org.apache.jmeter.testelement.WorkBench
required-type : org.apache.jmeter.testelement.WorkBench
converter-type : org.apache.jmeter.save.converters.TestElementConverter
path :
/jmeterTestPlan/hashTree/org.apache.jmeter.testelement.WorkBench
line number : 3
class[1] : org.apache.jorphan.collections.ListedHashTree
converter-type[1] : org.apache.jmeter.save.converters.HashTreeConverter

message : null : null
---- Debugging information ----
cause-exception : java.lang.NullPointerException
cause-message : null
class : org.apache.jmeter.testelement.WorkBench
required-type : org.apache.jmeter.testelement.WorkBench
converter-type : org.apache.jmeter.save.converters.TestElementConverter
path :
/jmeterTestPlan/hashTree/org.apache.jmeter.testelement.WorkBench
line number : 3
class[1] : org.apache.jorphan.collections.ListedHashTree
converter-type[1] : org.apache.jmeter.save.converters.HashTreeConverter

cause-exception :
com.thoughtworks.xstream.converters.ConversionException
cause-message : null : null
first-jmeter-class :
org.apache.jmeter.save.converters.HashTreeConverter.unmarshal(HashTreeConverter.java:65)
class : org.apache.jmeter.save.ScriptWrapper
required-type : org.apache.jmeter.testelement.WorkBench
converter-type : org.apache.jmeter.save.ScriptWrapperConverter
path :
/jmeterTestPlan/hashTree/org.apache.jmeter.testelement.WorkBench
line number : 3
version : 2.11 r1554548

2014/06/27 19:19:16 WARN - jmeter.gui.action.Load: Unexpected error
org.apache.jmeter.exceptions.IllegalUserActionException: Empty TestPlan -
see log file
at org.apache.jmeter.gui.action.Load.insertLoadedTree(Load.java:174)
at org.apache.jmeter.gui.action.Load.loadProjectFile(Load.java:136)
at org.apache.jmeter.gui.action.Load.loadProjectFile(Load.java:105)
at org.apache.jmeter.gui.action.Load.doAction(Load.java:92)
at
org.apache.jmeter.gui.action.ActionRouter.performAction(ActionRouter.java:81)
at
org.apache.jmeter.gui.action.ActionRouter.access$000(ActionRouter.java:40)
at org.apache.jmeter.gui.action.ActionRouter$1.run(ActionRouter.java:63)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:312)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:733)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:694)
at java.awt.EventQueue$3.run(EventQueue.java:692)
at java.security.AccessController.doPrivileged(Native Method)
at
java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:703)
at
java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at
java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at
java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)

How can this be fixed?

Cheers,

H.