i have been getting this error when i was doing ant installer.izpack, taskdef class net.sf.launch4j.ant.Launch4jTask cannot be found

i am getting this error when i was doing ant installer.izpack

error

taskdef class net.sf.launch4j.ant.Launch4jTask cannot be found using the classloader AntClassLoader[]

<taskdef name="launch4j"

                                         classname="net.sf.launch4j.ant.Launch4jTask"

                                         classpath="${launch4j.dir}/launch4j.jar:${launch4j.dir}/lib/xstream.jar" /> this line i  have been getting taskdef class net.sf.launch4j.ant.Launch4jTask cannot be found using the classloader AntClassLoader[]

but  i have used my manual lication of  Launch4j given below

                    <property name="launch4j.dir" location="c:\\ProgramFiles\\Launch4j" />

i am waiting for your reply