title: System.BadImageFormatException: How to fix .NET version mismatch?
body: <p>I wrote a dll in VS 2005 that will be loaded by another program that was developed in VS 2003. When that program tries to load my dll, it throws a <code>System.BadImageFormatException: The format of the file 'Foo.dll' is invalid</code>.</p>
  
  <p>I searched SO and Google, and it seems that the different version of .NET is the culprit. My question is: How do I fix this?</p>
  
  <p>(I cannot modify the program developed in VS 2003.)</p>