title: Calling an x64 assembly via COM from a 32 bit App
body: <p>Short question : is it possible (on an x64 OS of course) ? If not, why exactly ? </p>
  
  <p>I have developed a c# plugin dll for excel 32.</p>
  
  <p>When compiled in x86 it works fine.</p>
  
  <p>When compiled in x64 the COM call fails.</p>
  
  <p>Do I need a 64 bit version of excel ?</p>
  
  <p>I thought COM was agnostic of compiling architecture and made communication possible between dlls developed in different technologies and having different architectures, but I guess the latter is wrong.</p>
  
  <p>I guess an x64 bit dll can obviously not be called via COM (or else) from a 32-bit app.</p>