Here's the FAQ:
The debug steps in that can tell you if the Revo shell extension is being tried (and just not returning any menu items) or if it isn't being tried at all for some reason.
It also links to a tool called ShellExView which can be used to see which shell extensions are on the system, look up their GUIDs, enable/disable them, and so on.
A couple of things: Make sure you are not running the whole Opus process elevated as admin. (Admin Mode to elevate individual windows is fine, but don't run dopus.exe itself elevated.) And reinstalling Revo Installer may be worth a try to see if it repairs things.
As a more general note, we do not recommend using special uninstallers with Opus. Opus's uninstaller does everything that should be needed itself, and any 3rd party tool that tries to second-guess things is more likely to cause a problem than improve things, in our experience.