To clean your PC, I recomend CCleaner. Yes, it's free and do a good job.
JNLP errors are Java related.
Your installation of Java seems to be corrupted. Get a fresh copy of the Java run time and reinstall.
Java Run Time Library are available for free.
It's also possible that you try to use some Java application and that this application have a problem. Here, also, you should look at reinstalling the application.