title: C# "Register COM interop" option is disabled
body: <p>I am trying to create DLL out of my C# code, I found some <a href="http://richnewman.wordpress.com/2007/04/15/a-beginner%E2%80%99s-guide-to-calling-a-net-library-from-excel/" rel="noreferrer">links</a> that guides me to create my DLL file and use it in Excel as I wanted. One of the steps is to check the "Register COM interop" check box in the Build tab of the project. </p>
  
  <p>Unfortunately, <strong>this checkbox is always disabled</strong>! Does anyone know how to enable it ? I am using VS 2010.</p>