Its amazing how fast Java is updating their minor versions and leaving some very angry customers behind. Version 1.6.15 broke the Java WebStart feature of updating the clients when releasing a new version. Java WebStart technology allows user to start application software for Java Platform from the Internet using web browser.
Unlike Java applets, Web Start applications do not run inside the browser, and the sandbox in which they run need not have as many restrictions, although this can be configured. Web Start has an advantage over applets in that it overcomes many compatibility problems with browsers’ Java plugins and different JVM versions. On the other hand, Web Start programs cannot communicate with the browser as easily as applets. To assist migration, users can also invoke a Java Applet as a Java Web Start application.
Java 1.6 update 19 which released a few minutes back has an interesting security warning dialog box that appears while running a Java based applet or application:-
This is due to the Java version upgrade to minor version 19. They have added this new “feature” : http://www.java.com/en/download/help/error_mixedcode.xml
You will have to decide which is the best setting for you. I would suggest we select point 2 as a workaround for now.