Unable to use workItemPublisher ANT call

I am trying to publish work items in build result.
For this I am using Ant call workItemPublisher but with no success.

<taskdef name="workItemPublisher" classname="com.ibm.team.build.ant.task.WorkItemPublisher" />
<workItemPublisher repositoryAddress="${repositoryAddress}"
          userId="${userId}"
          passwordfile="${passwordfile}"
          buildResultUUID="${buildResultUUID}"
          inputFileType="WORKITEM"
          filePath="WorkItemID.txt" />

RTC Build toolkit Version: 4.0.5
IBM JDK version: 6.0.14.20130926 (32 bit)

Error occurs on running the above script:
{taskdef class com.ibm.team.build.ant.task.WorkItemPublisher cannot be found
 using the classloader AntClassLoader[]}

Any clue?