Registering COM Add-In on 64 bit Windows (with NSIS / Wow6432Node)

If you like to register a COM add-in with a custom installer (instead of using RegAsm.exe), you can generate the keys using RegAsm.exe with the /regfile option. Thus, a straight forward way to register a COM add-in using NSIS is as follows:
  1. Use RegAsm.exe with the option /regfile to generate a list of registry entries.
  2. Create an NSIS script with the corresponding WriteRegStr entries to create these registry entries.

However, this method may not work if you like to use the installer on a 64 bit Windows 7 system to register the COM add-in for 64 bit applications. On a 64 bit system you will find some of your keys registered in the Wow6432Node, which is the part for 32 bit applications and not seen by 64 bit applications.
A workaround may be to use DLL host, however this workaround should only be used if your COM add-in is 32 bit only. The workaround will also work for COM add-ins which are 64 bit and 32 bit (compiled as "AnyCPU"), but performance will be poor.

The problem here is that NSIS creates a 32 bit installer which - per default - writes certain keys to the Wow6432Node (i.e. it registers the COM add-in for 32 bit applications). If you like to register the COM add-in for 64 bit applications (too) you have to register (again) using SetRegView 64 prior registration (search the internet for "NSIS SetRegView 64").

Note that the two version of RegAsm (one in Frameworks and one in Frameworks64) export the same registry entries when used with /regfile, but, writing to the registry, they write to the 32 bit or 64 bit view respectively.

See also and note that registry reflection was removed in Windows 7 (see )