IIS error, Unable to start debugging on the webserver

There may be many reasons for the above problem.

You need to check this:- Unable to Start Debugging on the Web Server

On a side note:- Go to IIS and check that the App Pool you are using is started.

Try this from your command line:-

cd %windir%\Microsoft.NET\Framework\v4.0.30319aspnet_regiis.exe -i

There are multiple solution of this problem, in my case I changed my machine's password but forget to change it in the process model identity of Advance setting of that Application pool.

Later IISRESET did the trick for me.

Just an update as I hit this issue and all of the settings in both Visual Studio and IIS seemed to be correct.

What actually worked for me was simply running Visual Studio as an administrator - I'm guessing that there is a permission that needs to be set somewhere, but I have no idea what or where.

Also a point to note is that I configured all my websites to use the DefaultAppPool in IIS which at the time was ASP.NET V2, then installed .NET 4 and the DefaultAppPool was converted to .NET4 so none of the sites would compile (that caused me a small amount of swearing)

Hope that helps someone