Most people just use the Mac and never really have to think about how the underlying applications and services operate. You point, click, and things just happen. The Mac so rarely needs "fixing" that its users never have to learn how. So when something "core" breaks in OS X it's a pain to repair.
Apple recently released Java SE 6.0 for OS X. This release offers the usual gambit of bug fixes, performance improvements, and tons of other items that most users will want. Unfortunately on some systems when you install SE 6.0 the "Open With..." associations between Java Web Start and ".jnlp" files are lost. When you attempt to launch a Web Start application you will see something like...
To fix this we need to reconnect ".jnlp" file types with "Java Web Start.app". To do so...
1. Find any .jnlp file you have saved on your system. They are usually in the "Downloads" directory managed by your browser (Your using Safari right? It's best imo!).
2. Select the .jnlp and press COMMAND-I to pull up the Info window.
3. If you are reading this then you probably will not see "Java Web Start.app" under the "Open with:" but rather some other app like "Preview". We need to change this setting to point to...
/System/Library/CoreServices/Java Web Start.app
Don't forget to click "Always Open With".
All set! You should be able to launch your StealthWatch UI along with any other Web Start apps you might use.