Thanks for checking those things.
I've attached two small programs which will do another test, which is more like what Visual Studio does (they both call the SHOpenFolderAndSelectItems API):
TestExplorerReplacement.zip (67.1 KB)
If you run TestExplorerReplacement_32bit.exe then you should get an Opus window with C:\Windows\write.exe selected.
If you run TestExplorerReplacement_64bit.exe then you should get an Opus window with C:\Windows\notepad.exe selected.
If they both open Opus then there's something strange going on, but if either one opens File Explorer instead of Opus then it's possible Opus's DLLs aren't registered properly.
[ul][li]If that's the case, try reinstalling Opus over the top of itself. (Don't uninstall first; that would wipe your config and isn't necessary.)
[/li]
[li]Another thing that's worth a try is to disable Explorer Replacement via Preferences, click OK, then re-open Preferences, re-enable Explorer Replacement, and click OK again. That will re-write some other registry settings which may not be as they should be.[/li][/ul]