Unable to start debugging on the web server. Could not start ASP.NET debugging VS 2010, II7, Win 7 x64

I am running Visual Studio 2010 (as Admin), IIS 7 on Windows 7 x64. I am able to run the ASP.NET web site in IIS 7 without debugging just fine, but when I press F5 to debug it, I get:

Unable to start debugging on the web server. Could not start ASP.NET debugging. More information may be available by starting the project without debugging.

Unfortunately the help link is not helping me much and leads down a heck of a large tree of things.

I checked the following:

• Security requirements — I don't recall having to do anything special before. The worker process in IIS7 is w3wp.exe. It says that if it's running as ASPNET or NETWORK SERVICE I must have Administrator privileges to debug it. How do I find out if I need to change something here?

• Web site Property Pages > Start Options > Debuggers > ASP.NET is checked. Use custom server is set to the URL of the site (which works fine without debugging).

• Debugging is enabled in web.config.

• Application is using ASP.NET 3.5 (I want to move to 4.0 eventually but I have some migration to deal with).

• Application pool: Classing .NET AppPool (also tried DefaultAppPool).

Any ideas where I can check next?

Surely it shouldn't be that hard to install IIS, VS, create a web site, and start testing it?

Thanks in advance.

Try going to IIS and checking to make sure the App Pool you are using is started. A lot of times, you will produce an error that shuts down the app pool. You just need to right click and Start and you should be good to go.

Turns out that the culprit was the IIS Url Rewrite module. I had defined a rule that redirected calls to Default.aspx (which was set as the start page of the web site) to the root of the site so that I could have a canonical home URL. However, apparently VS had a problem with this and got confused. This problem did not happen when I was using Helicon ISAPI_Rewrite so it didn't even occur to me to check.

I ended up creating a whole new web site from scratch and porting projects/files over little by little into my solution and rebuilding my web.config until I found this out! Well, at least now I have a slightly cleaner site using .NET 4.0 (so far, hopefully I won't run into any walls)--but what a pain!