1. To Get Debugging Working

Need a web.config file in the root directory.
Then need to make sure that there's a line like this:-

                                                     
<customErrors mode="Off" />
                                                     

needs to be "Off" for errors to appear
NB: Debugging slows down the website, so should be turned off when site is live.  I think this setting is "On" (confusingly!)