http://bugs.winehq.org/show_bug.cgi?id=29941
--- Comment #11 from Hans Leidekker hans@meelstraat.net 2012-02-21 15:15:34 CST --- (In reply to comment #10) ...
Thanks for pointing that out! With ntlm_auth installed the installation succeeds in win32 mode, but still fails otherwise.
Looks like the 64-bit version fails when trying to load a 64-bit custom action dll. We load custom action dlls in-process but this installer executable is 32-bit, so the dll can't be loaded. It works on native because it runs custom actions in a separate 64-bit server process.