targetFramework="4.0" making the debugger not work

...at an ASP.NET web site? Is the problem this part of Web.config?

<system.web>
   <compilation debug="true" targetFramework="4.0"/>

 
 

If so right-click on the project and prick "Property Pages" in Visual Studio 2013. Click the "Build" menu item at the left and then change the "Target Framework" to: ".NET Framework 4"