I had this same problem when I installed and tested URLSnooper today (for the first time btw). Every attempt to find and test a network adaptor resulted in a red string saying "Failed", even though the progress messages during the test showed that multiple packets were being exchanged through that adaptor.
Switching to 'Advanced Mode' showed me that the test is based on finding a specific string (by default "/* breadcrumbs */") on a specific web page (by default "http://www.google.com/css/screen.css
"), and when I tested the same default URL in Firefox I found that the page no longer exists (404 message), which is not at all surprising since it belongs to google. They have every right to alter their pages as they please. It would be better for the test URL to refer to some page over which you (the programmer I mean) can exercise some control, over both its continued existence and its specific content.
Editing the test URL and the test string to suit one of the pages I commonly used, which is very stable, I was able to use the automatic test function successfully, so I've already solved the problem for my own needs. But to aid future users, it would be better to modify the release package, to use an existing (and hopefully stable) web page for these tests.
Best regards: dlanor