The builder cannot build plugins/org.eclipse.jdt.ui
My build.properties file:
J2SE-1.4=/usr/share/java/ant-commons-logging.jar:/usr/share/java/libgcj.jar:/usr/share/java/ant-junit.jar:/usr/share/java/:libgcj-4.2.3.jar:/usr/share/java/ecj.jar:/usr/share/java/libgcj-tools-4.2.3.jar:/usr/share/java/gnome-java-bridge.jar:/usr/share/java/ant-apache-resolver.jar:/usr/share/java/libgcj-4.2.jar:/usr/share/java/ant-trax.jar:/usr/share/java/ant-bootstrap.jar:/usr/share/java/cp-tools-0.0.20020812.jar:/usr/share/java/libgcj-tools-4.2.jar:/usr/share/java/ant-nodeps.jar:/usr/share/java/xercesImpl.jar:/usr/share/java/eclipse-ecj.jar:/usr/share/java/ant-swing.jar:/usr/share/java/ant-apache-regexp.jar:/usr/share/java/ant-jmf.jar:/usr/share/java/ant-launcher.jar:/usr/share/java/ant-apache-bcel.jar:/usr/share/java/ant-1.7.jar:/usr/share/java/xmlParserAPIs.jar:/usr/share/java/ant-apache-oro.jar:/usr/share/java/ant-commons-net.jar:/usr/share/java/ant-jsch.jar:/usr/share/java/cp-tools.jar:/usr/share/java/ant.jar:/usr/share/java/ant-apache-log4j.jar:/usr/share/java/ant-apache-bsf.jar:/usr/share/java/ant-javamail.jar:/usr/share/java/ant-jdepend.jar:/usr/share/java/libintl.jar:/usr/share/java/jaxp-1.3.jar:/usr/share/java/ant-antlr.jar
J2SE-1.5=/usr/lib/jvm/java-6-openjdk/jre/lib/jsse.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/resources.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/jce.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/compilefontconfig.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/management-agent.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/ext/gnome-java-bridge.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/ext/sunjce_provider.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/ext/dnsns.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/ext/localedata.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/ext/sunpkcs11.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/about.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/charsets.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/rt.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/security/US_export_policy.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/security/local_policy.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/im/indicim.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/im/thaiim.jar
JavaSE-1.6=/usr/lib/jvm/java-6-openjdk/jre/lib/jsse.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/resources.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/jce.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/compilefontconfig.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/management-agent.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/ext/gnome-java-bridge.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/ext/sunjce_provider.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/ext/dnsns.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/ext/localedata.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/ext/sunpkcs11.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/about.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/charsets.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/rt.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/security/US_export_policy.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/security/local_policy.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/im/indicim.jar:/usr/lib/jvm/java-6-openjdk/jre/lib/im/thaiim.jar
It's interesting that you have a problem here, since the legacy package compiles this fine.
Can you verify that the right values (1.3 and 1.2 respectively) are being passed to the java compiler for that plugin?