Does a COM DLL have to be compiled and registered for each bit edition?
See the question and my original answer on StackOverflowNo, you can keep the .DLL compiled as "Any CPU" (in fact I certainly recommend it as long as you can), but you must register it in each version of the registry, so for example using regasm:
64-bit:
c:\Windows\Microsoft.NET\Framework64\v4.0.30319\RegAsm.exe ClassLibrary1.dll /codebase /tlb
32-bit:
c:\Windows\Microsoft.NET\Framework\v4.0.30319\RegAsm.exe ClassLibrary1.dll /codebase /tlb