Today when I'm trying to install Adobe Flash Player ActiveX 9 for some application, there's an error expected
error 1904 C:\Windows\syswow64\macromed\flash\flash9d.ocx failed to register. HRESULT 2147220473
really confused, because I didn't know why this is happen. FYI I use Windows 7 64-bit. After trying about 3 hours (it waste my time so much) finally I found the solution.
1. Uninstall your Adobe Flash player activeX, or you can download the adobe flash player uninstaller here.
2. Clean your registry using CCleaner, because maybe there's some data left on registry.
3. Restart Your Computer
4. Close all of your application and install your Adobe Flash Player 9 ActiveX
5. When you install it, maybe there's still an error 1904, but don't worry about that. Just finish your installation.
6. Go to Command Prompt, and change directory into C:\Windows\sysWOW64\macromed\flash.
7. Type regsvr32 flash9d.ocx.
This solution works like a charm for me. Maybe you can try this solution perhaps works for you too.