为什么我不能调试我的asp.net网络应用程序

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.When I add a breakpoint and hit F5 to run in th