I have been working with VS2010 and ASP.Net 4.0 for quite some time now. Every time i create a web application, I just use the handy feature of Visual Studio of creating virtual directory for web application. Last week I was manually creating virtual directory for a web application using IIS manager. Since the application was targeting ASP.Net 2.0, so from ASP.Net tab of IIS, I selected V2.0 framework. Now there is a confirmation dialog box that comes up when you change ASP.Net framework.
Changing the Framework version requires a restart of the W3SVC service. Alternatively, you can change the Framework version without restarting the W3SVC service by running: aspnet_regiis.exe -norestart -s IIS-Viirtual-Path Do you want to continue (this will change the Framework version and restart the W3SVC service)?
Everything is good so far. Moment i accessed the application in browser, I got the following error message.
Server Error in '/Foo' Application.
The application domain or application pool is currently running version 4.0 or later of the .NET Framework. This can occur if IIS settings have been set to 4.0 or later for this Web application, or if you are using version 4.0 or later of the ASP.NET Web Development Server. The <compilation> element in the Web.config file for this Web application does not contain the required 'targetFrameworkMoniker' attribute for this version of the .NET Framework (for example, '<compilation targetFrameworkMoniker=".NETFramework,Version=v4.0">'). Update the Web.config file with this attribute, or configure the Web application to use a different version of the .NET Framework.
I was little surprised because I never configured virtual directory for this application to use ASP.Net 4.0. I fired up IIS manager and went to ASP.Net tab. There it was, the application was configured to use ASP.Net 4.0. So I changed it back to use ASP.Net 2.0. Accessed the application in browser and got the same error again. I experimented with the drop down box for ASP.Net version in IIS manager. The application will get configured to use ASP.Net 4.0 no matter what option I picked from the drop down box. It seems that this is some bug in beta version of Visual Studio 2010 installation.
For now the work around I have been using is to let Visual Studio create virtual directory for my web application. It targets the correct ASP.Net version and modifies IIS meta data correctly.