Java SE (Java Platform, Standard Edition)

Hi all !

I try to run my client-application through Java Web Start. I've created and signed one jar file which contains several classes. So when I try to run applikation after accept certificate I have this exception :

An error occurred while launching/running the application.

Title: aaa
Vendor: bbb
Category: Unexpected Error

Unexpected exception: java.lang.reflect.InvocationTargetException

java.lang.reflect.InvocationTargetException
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.lang.reflect.Method.invoke(Unknown Source)
	at com.sun.javaws.Launcher.executeApplication(Unknown Source)
	at com.sun.javaws.Launcher.executeMainClass(Unknown Source)
	at com.sun.javaws.Launcher.continueLaunch(Unknown Source)
	at com.sun.javaws.Launcher.handleApplicationDesc(Unknown Source)
	at com.sun.javaws.Launcher.handleLaunchFile(Unknown Source)
	at com.sun.javaws.Launcher.run(Unknown Source)
	at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.ClassFormatError: Incompatible magic value 1347093252 in class file Klient/KlientDef
	at java.lang.ClassLoader.defineClass1(Native Method)
	at java.lang.ClassLoader.defineClass(Unknown Source)
	at java.security.SecureClassLoader.defineClass(Unknown Source)
	at com.sun.jnlp.JNLPClassLoader.defineClass(Unknown Source)
	at com.sun.jnlp.JNLPClassLoader.access$100(Unknown Source)
	at com.sun.jnlp.JNLPClassLoader$1.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at com.sun.jnlp.JNLPClassLoader.findClass(Unknown Source)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	at com.sun.jnlp.JNLPClassLoader.loadClass(Unknown Source)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	at java.lang.ClassLoader.loadClassInternal(Unknown Source)
	at Klient.KlientRun.main(KlientRun.java:19)
	... 11 more

JNLP file : 

<?xml version="1.0" encoding="utf-8"?>
<!-- JNLP File for SwingSet2 Demo Application -->
<jnlp
  spec="1.0+"
  codebase="http://localhost:999/PracaDyplomowa/"
  href="klient.jnlp">
  <information>
    <title>aaa</title>
    <vendor>bbb</vendor> 
    <offline-allowed/>
  </information>
  <security> 
      <all-permissions/> 
  </security> 
  <resources>
	<j2se version="1.5"/>
	<jar href="AplikacjaKlienta.jar"/>
  </resources>
  <application-desc main-class="Klient.KlientRun"/>
</jnlp> 

I've looked about this problem in forum but I didn't fount any hints. Can anyone help me?

Thanks
Chudzik