selectionFailure fault while updating the output variable in Java Embedding

In my java embedding i was updating the outvariable of the bpel  using the setVariable method.But i was getting the following error in doing so.

{{http://docs.oasis-open.org/wsbpel/2.0/process/executable}selectionFailure}

messageType: {{http://schemas.oracle.com/bpel/extension}RuntimeFaultMessage}
parts: {{
summary=

 
There can be 2 reasons for this either the Xapth expression is wrong.

Second in 11g before setting the value of the outvariable in java embedding it should be intialized.Put an assign activity before java embedding and  initialize the variable and than set the value in java embedding and it will work.