64 Bit MSI Custom Actions
Acresso has answered my question regarding 64 bit custom actions. The bottom line is that they are not allowed.
You are correct that you cannot call a 64 bit dll from a managed custom action, however this is not dependent on setup.exe or any prerequisites.
Windows Installer does not have a managed custom action type so InstallShield wraps the managed dll in a native 32 bit dll. The issue is then that the 32 bit wrapper can’t call into a 64 bit dll and so there is no way to do this. So the technical restriction is that our 32 bit wrapper is unable to call into 64 bit dlls.
It is possible to launch a 64 bit executable from a custom action and do whatever is required from the 64 bit exe.
Additionally, you can create a class that derives from the System.Installer class and set the “.Net Installer” property within Install Shield, but it is more difficult to control when the code is called.