If you get this error you must run your application through external tool configuration in Eclipse. Here is the proof. In connection with JavaFX in Eclipse. @Tom also said it’s now fixed in nightly. You should’t experience this problem anymore.

BUILD FAILED
C:\Users\xxx\workspace\kjh\build\build.xml:13: The following error occurred while executing this line:
jar:file:/C:/Program%20Files%20(x86)/Java/jre7/lib/ext/ant-javafx.jar!/com/sun/javafx/tools/ant/antlib.xml:13: typedef A class needed by class com.sun.javafx.tools.ant.Application cannot be found: org/apache/tools/ant/types/DataType
using the classloader AntClassLoader[C:\Program Files (x86)\Java\jre7\lib\jfxrt.jar]