Ant/Build a JAR : Build failed, Reference task.path not found

I'm working on a project with a build.xml to generate a JAR file. When I try to build it I get this error:

Buildfile: D:\xxxxx\trunk\project-java\build.xml

BUILD FAILED D:\xxxxxtrunk\project-java\build.xml:25: Reference task.path not found.

Total time: 140 milliseconds

Build.xml with the line where it crashes.

<?xml version="1.0"?>
<project name="xxxxx" default="prepare-release" basedir=".">

<property name="project.dir" value="."/>
<property file="${project.dir}/build.properties"/>
<property file="${project.dir}/svn.properties"/>

<property name="dist.dir" value="${project.dir}/dist"/>

<property name="build.dir" value="${project.dir}/build"/>
<property name="src.dir" value="${dist.dir}/${dist.type}/src"/>
<property name="release.dir" value="${project.dir}/release"/>



<!-- load svn tasks -->
// Pb on this line
<typedef resource="org/tigris/subversion/svnant/svnantlib.xml" 
     classpathref="task.path" />

What can it be? Thanks for your help.