Running application in netbeans results in NoSuchMethodError

While I'm running a simple application in my Netbeans 6.9.1,it's showing "task running, click for details" for a long time .and also there is an error "unexpected exception" in the bottom of the netbeans when I'm clicking that:

NoSuchMethodError: org.apache.tools.ant.util.FileUtils.getFileUtils()Lorg/apache/tools/ant/util/FileUtils;

This error is coming. Few days before this application executed well, but now this erro开发者_运维技巧r for all applications.The main error is it's not running,but it's showing "running" for a long time..

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You should move to the newer or at least stable version of netbeans (from what I can see you are using a beta version '6.9beta'. Download the latest stable release of netbeans and open your project there.