Problems running Applet

Hello!
I have some problems with my Appltes in InternetExplorer 6.0.

When I use Suns plugin everything works fine, but when I deactivate suns plugin and use Microsofts VM I always get this error. It doesn't matter if it is in a jar file or not:

Microsoft (R) VM for Java, 5.0 Release 5.0.0.3810
==============================================
?  hjäp
c  rensa
f  kör slutförare
g  samla in skräp
m  minnesanvändning
q  avsluta
t  lista trådar
==============================================
Error loading class: MyApplet5a
java.lang.NoClassDefFoundError
java.lang.ClassNotFoundException: MyApplet5a
    at com/ms/vm/loader/URLClassLoader.loadClass
    at com/ms/vm/loader/URLClassLoader.loadClass
    at com/ms/applet/AppletPanel.securedClassLoad
    at com/ms/applet/AppletPanel.processSentEvent
    at com/ms/applet/AppletPanel.processSentEvent
    at com/ms/applet/AppletPanel.run
    at java/lang/Thread.run

The APPLET-tag looks like this:
<APPLET CODE="MyApplet5a" ARCHIVE="applets.jar" WIDTH="200" HEIGHT="200"></APPLET>

So if any one know what the problem is please let me know. After all the Idea with Java is that it should be plattform independent, write once run every where.

Best regards
Fredrik