<p>When I add a breakpoint and hit F5 to run in the debugger (I am using my debug build), a dialog pops up telling my my web.config file does not have debug=true in it (which is does) and I get 2 choices a) run without the debugger or b) let visual studio update my web.config file. If I choose b) the web.config is updated badly and nothing will work. If I choose a) then the site appears and I can test it out, but no debugging.</p>

<p>I am an experienced developer, but I have never used visual studio and asp.net for web development before, so I am feeling rather frustrated by all the walls it is putting up to prevent me working.</p>

<p>So far I have not been able to use the debugger. Is there something totally obvious that I am missing? What would you check if it was happening to you?</p>

Open web.config manually and make sure the following line is in there
```
```
<compilation defaultLanguage="c#" debug="true" />
```
```
Now you should be able to debug from VS. If this does not work I suggest that you recreate the project.
EDIT: perhaps from what you say it could be that web.config is screwed up, e.g.contains invalid xml, no closing tag for some element etc.