Java Applet on Windows 7

Hello

When I surf to my gallery2 on Windows 7 with IE 8 or FireFox 3.5.5, I can't seem to get the Java Upload Applet working. When I surf to the same gallery2 on a Windows XP computer it works like a charm. I get the following Java error in console (using Java 6 update 17):

load: class com.gallery.GalleryRemote.GRAppletMini not found.
java.lang.ClassNotFoundException: com.gallery.GalleryRemote.GRAppletMini
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)
Exception: java.lang.ClassNotFoundException: com.gallery.GalleryRemote.GRAppletMini

Any ideas ?

Gallery version (not just "2"): 2.3
PHP version (e.g. 5.1.6): 5.2.11
Webserver (e.g. Apache 1.3.33): IIS
Database (e.g. MySql 5.0.32): SQL Server 2005
Operating system (e.g. Linux): Windows 7
Browser (e.g. Firefox 2.0): IE 8 & FireFox 3.5.5