You have tryied to load a bad URL. there are various reasons for it, the most common are:
Thinking about it there may be even more. The suggestion is to try to load the very same URL using your preferred browser and see what happens. Bear in mind that if you are tryng to load bleading edge HTML (yes, really bleading) you will NOT be able to do it in here. This is a portable html viewer, it works in any platform that supports Java > 1.3.2.