Can you provide build number you're using and fragment of code, please? 

no problem, here some infos about versions:

Product Version: NetBeans IDE 6.0.1 (Build 200801291616)
Java: 1.6.0_02; Java HotSpot(TM) Client VM 1.6.0_02-b06
System: Windows XP version 5.1 running on x86; Cp1252; de_DE (nb)

and here the sourcecode (after renaming -> includes the wrong statement yet in line 5):

package de.cbg.streams;

//@author MH

import de.cbg.datenströme.*;
import java.io.File;

public class DateiBeobachter implements Runnable {
    String filename;
    File file;
    Runnable info;
    
    DateiBeobachter(String Filename, Runnable r){
        this.filename = Filename;
        file = new File(Filename);
        info = r;
    }
    
    DateiBeobachter(File mFile, Runnable r){
        this.file = mFile;
        info = r;
    }
    
    @Override public void run(){
        long last = file.lastModified();
        
        while(true){
            if(last < file.lastModified()){
                info.run();
                last = file.lastModified();
            }else
                System.out.println(file.getName());
            
            try{
                Thread.sleep(1000);
            }
            catch(InterruptedException e){}
        }
    }
    
    public static void main(String[] args) {
        Thread db = new Thread(new DateiBeobachter("c:/test.txt", new InfoMe()));
        db.start();
    }
}

class InfoMe implements Runnable{
    @Override public void run(){
        System.out.println("Datei geändert");
    }
}

Thanks for info, it's duplicate of issue 128830, which should be already fixed in the upcoming version

*** This issue has been marked as a duplicate of 128830 ***