should be using JavaSE-1.6 VM, and .classpath, codegen.targetPlatform, compliance and source should also all be 1.6
<?xml version="1.0" encoding="UTF-8"?>
<classpath>
<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-1.6"/>
<classpathentry kind="con" path="org.eclipse.pde.core.requiredPlugins"/>
<classpathentry kind="src" path="src"/>
<classpathentry exported="true" kind="lib" path="lib/commons-codec-1.3.jar"/>
<classpathentry exported="true" kind="lib" path="lib/commons-httpclient-3.1.jar"/>
<classpathentry exported="true" kind="lib" path="lib/commons-logging-1.1.jar"/>
<classpathentry kind="output" path="bin"/>
</classpath>