title: Problem with built assembly not matching source when debugging under IIS 7.5
body: <p>I have a problem debugging a web forms application that is configured to use IIS for debugging, under Windows 7 and Visual Studio 2010.  An example has just occurred, where I make a change to the code behind for a web form, save, and apparently rebuild before starting the app using F5.  </p>
  
  <p>The app starts, and I get an error message trying to do something in the app.  I tell the debugger to break when an exception is thrown and try my task again, only to be told</p>
  
  <p><em>The source file is different from when the module was built.</em></p>
  
  <p>where the module is <code>C:\Windows\Microsoft.NET\Framework64\v2.0.50727\Temporary ASP.NET Files\root\9d7b45ca\11a98b19\assembly\dl3\5e6cf0b2\636409d4_dfeecb01\PerfixEMS_Admin.DLL</code></p>
  
  <p>The physical folder for my test web site is set to the web application project's source folder, so I have always assumed that IIS will look in the <code>bin</code> folder for required assemblies, and these will be rebuilt as expected.  Why is this not happening?</p>