I tested your SimpleBrowser and, as you can see in your server's log, I had no errors.

I had to create a second button to load the URL with JavaScript because I don't have some of your components but the result is the same.
I noticed that you show the error message for all resources and your URL loads some content related to a chat box from another domain.
Perhaps the error message belongs to some resource from that domain.
Some other wild guesses :
- Are you connected through a proxy server?
- Are you waiting until all the document is fully loaded (chat box included) before loading the new URL?