Invalid handle runtime error

Question

Enter name of file:
Exception in thread "main" java.io.IOException: The handle is invalid
at java.io.FileInputStream.readBytes(Native Method)
at java.io.FileInputStream.read(Unknown Source)
at java.io.BufferedInputStream.read1(Unknown Source)
at java.io.BufferedInputStream.read(Unknown Source)
at sun.nio.cs.StreamDecoder.readBytes(Unknown Source)
at sun.nio.cs.StreamDecoder.implRead(Unknown Source)
at sun.nio.cs.StreamDecoder.read(Unknown Source)
at java.io.InputStreamReader.read(Unknown Source)
at java.io.BufferedReader.fill(Unknown Source)
at java.io.BufferedReader.readLine(Unknown Source)
at java.io.BufferedReader.readLine(Unknown Source)
at crapo.main(crapo.java:15)
Tool completed with exit code 1
import java.io.*;
public class crapo{
public static void main(String[] args) throws IOException {
BufferedReader keys = new BufferedReader(
new InputStreamReader( System.in ));
System.out.println("Enter name of file: ");
String fileName = keys.readLine();
}

Answer 1

Maybe I just figured something out:
First of all, most of the Functions, that cause the Error, are in Timer-Callbacks (at this state of development, ALL of them)
So I just added a Test-Function in a normal Button-Callback, which contains a "GetCtrlArrayItem"-Function, and this specific Line does NOT cause an Error... (Or at least it does not occur in the Error-List, when clicking "continue" in debugging-mode). Somehow the Timer-Callbacks seem to be called, when closing the Application...
BUT: this happens when I don't do anything in the Application, and the all Timers are Disabled, until some Buttons are pushed (so when I close the application right after opening it, they still should be disabled) 
@ Wolfgang:
After discarding I do not want to use one of the handles, or at least I'm not doing that purposely
@ Roberto:
Actually I am only discaring the MainPanel-Handle in the Main.uir (and one other Panel, but the error occurred before implementing that other panel). Do all Handles (PanelHandles as well as ControlArrayHandles, TabPageHandles and so on) need to be discarded?
And no, I did not check the Variable Window, I was not aware of this possibility, I will try to figure that out.