title: cannot add a reference .NET
body: <p>I have a DLL which I would like to add as a reference to my project, but everytime I try to do it a dialog pops up telling me:</p>
  
  <blockquote>
    <p>The reference could not be added. Please make sure that the file is accesible, and that it is a valid  assembly or COM component.</p>
  </blockquote>
  
  <p>I have researched a little and found out that error is because the assembly is unmanaged by .NET and that I should use DLLImport Attribute, however, I have the same exact solution in another computer, and everythig just works fine. </p>
  
  <p>The difference is that the new computer I'm trying to add the reference is x64 and the old one is x86.</p>
  
  <p>I have both the x64 and x86 DLL's, and can't add any. Why is this happening?</p>