Salve sono di nuovo io.
Allora,
ditemi se ho fatto bene.

Ho compilato il tutto da riga di comando usando javac -d . FtpApplet.java
poi ho creato il JAR scrivendo jar cvf Ftp.jar pac/*.class

Tutto procede liscio.

Vado a creare un file index.html con dentro


Ma ricevo questo errore.
codice:
<applet code="pac.FtpApplet" archive="ftp.jar" width=800 height=600 alt="Necesita actualizar Java, utilice el link al final de la pįgina."></applet>
codice:
Java Plug-in 1.6.0_15
Uso della versione JRE 1.6.0_15-b03 Java HotSpot(TM) Client VM
Directory principale utente = D:

java.lang.ClassFormatError: Incompatible magic value 1347093252 in class file pac/FtpApplet
	at java.lang.ClassLoader.defineClass1(Native Method)
	at java.lang.ClassLoader.defineClass(Unknown Source)
	at java.security.SecureClassLoader.defineClass(Unknown Source)
	at java.net.URLClassLoader.defineClass(Unknown Source)
	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 sun.plugin2.applet.Plugin2ClassLoader.defineClassHelper(Unknown Source)
	at sun.plugin2.applet.Plugin2ClassLoader.access$400(Unknown Source)
	at sun.plugin2.applet.Plugin2ClassLoader$2.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at sun.plugin2.applet.Plugin2ClassLoader.findClassHelper(Unknown Source)
	at sun.plugin2.applet.Applet2ClassLoader.findClass(Unknown Source)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	at sun.plugin2.applet.Plugin2ClassLoader.loadCode(Unknown Source)
	at sun.plugin2.applet.Plugin2Manager.createApplet(Unknown Source)
	at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)
	at java.lang.Thread.run(Unknown Source)
Eccezione: java.lang.ClassFormatError: Incompatible magic value 1347093252 in class file pac/FtpApplet
Indago sull'errore.

Aiuti?