fo生成pdf文件,怎么总是提示这个错误?

[shuzhiguo]

import java.io.*;
import org.xml.sax.InputSource;
import org.xml.sax.XMLReader;
import org.apache.fop.apps.*;
import org.apache.avalon.framework.logger.*;

public class fottest {
public fottest(){

}
public static void main(String args[]) {
try {
Driver driver = new Driver();
driver.setInputSource(new InputSource ("test.fo"));
driver.setOutputStream(new FileOutputStream("txt.pdf"));
driver.setRenderer(Driver.RENDER_PDF);
driver.run();
}
catch( Exception e ){
e.printStackTrace();
}
}
}
fo文件存在,且在开发环境中已经加入了fop.jar,
但是总是提示以下这个错误,不知道为什么?好像在别人机子上就没有这个错误啊?
Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/avalon/framework/logger/Logger

[saucer]

it seems avalon-framework-*.jar is not on the classpath