Have you had a look here?
NullPointerException at FindAppletJDKLevel(unknown source) - Java Forums
// Json
Type: Posts; User: Json
Have you had a look here?
NullPointerException at FindAppletJDKLevel(unknown source) - Java Forums
// Json
Do you not have to specify the .class ending in the applet tag?
<html>
<head>
<title>Test Applet</title>
</head>
<body>
<APPLET code="main\UI.class" archive="test.jar" width="500"...