Error with ANT

I tried to build a service in AXIS2 using ANT and I get this error all the time. I am using JDK6. Any ideas please?

BUILD FAILED
java.lang.AbstractMethodError: javax.xml.parsers.SAXParser.getXMLReader()Lorg/xm
l/sax/XMLReader;
        at org.apache.tools.ant.util.JAXPUtils.getNamespaceXMLReader(JAXPUtils.j
ava:172)
        at org.apache.tools.ant.helper.ProjectHelper2.parse(ProjectHelper2.java:
185)
        at org.apache.tools.ant.helper.ProjectHelper2.parse(ProjectHelper2.java:
138)
        at org.apache.tools.ant.ProjectHelper.configureProject(ProjectHelper.jav
a:96)
        at org.apache.tools.ant.Main.runBuild(Main.java:683)
        at org.apache.tools.ant.Main.startAnt(Main.java:199)
        at org.apache.tools.ant.launch.Launcher.run(Launcher.java:257)
        at org.apache.tools.ant.launch.Launcher.main(Launcher.java:104)

Total time: 0 seconds
java.lang.AbstractMethodError: javax.xml.parsers.SAXParser.getXMLReader()Lorg/xm
l/sax/XMLReader;
        at org.apache.tools.ant.util.JAXPUtils.getNamespaceXMLReader(JAXPUtils.j
ava:172)
        at org.apache.tools.ant.helper.ProjectHelper2.parse(ProjectHelper2.java:
185)
        at org.apache.tools.ant.helper.ProjectHelper2.parse(ProjectHelper2.java:
138)
        at org.apache.tools.ant.ProjectHelper.configureProject(ProjectHelper.jav
a:96)
        at org.apache.tools.ant.Main.runBuild(Main.java:683)
        at org.apache.tools.ant.Main.startAnt(Main.java:199)
        at org.apache.tools.ant.launch.Launcher.run(Launcher.java:257)
        at org.apache.tools.ant.launch.Launcher.main(Launcher.java:104)
javax.xml.parsers.SAXParser.getXMLReader()Lorg/xml/sax/XMLReader;