Keep Coding

I have a uri / server error and I don't understand what it means.
my mapping looks like this:
app = webapp2.WSGIApplication([('/', MainPage), ('/fizzbuzz', FizzBuzzHandler),
],
debug=True)
and the error log on app engine is

Check the Logs Viewer. You can filter by Log Level == Error or Critical if you need to dig through a ton of lines.
There you can determine more about what went wrong in your requests.