One thing to check is that Opus is 'seeing' the Norton shell extension. That will tell us if the problem happens when Opus asks the shell extension to add its menu items, or if we aren't even reaching that point.
If you want to check that, please follow the steps in the Finding The Culprit section of this guide. (i.e. Turn on context_menu_debug, run DebugView and see what is output when you right-click a file.)
If you see some entries for Norton, one thing to check is that they're for the right version. (Maybe Opus is calling the old version of the shell extension, if the upgrade has left some old registry settings or something, and that's why it's not working.) It may be difficult to tell, depending on what the debug output says; a tool like ShellExView can be used to get more information about all the shell extensions, including the path to their DLLs which often reveals their version details.
If you see entries for Norton's shell extension when you right-click files, then Opus is calling it but it isn't adding anything to the menu for some reason. Norton will probably need to debug what's happening on their side if that is the case, since we can't see what's happening inside their code.
If you don't see any entries for Norton's shell extension, it may be registered in a way which Opus doesn't support. (There are so many different ways to do it, some undocumented, so it's possible there is one we have missed.) If that's the case, maybe Norton can look at what's changed between the old and new versions, in terms of how the shell extension is registered or which interfaces it expects to be used, and we can look into making Opus work with what they're doing if it's possible & makes sense.
Whether the problem turns out to be in Norton or Opus, if it's easy for us to add a fix or workaround then we'll usually do so, to get things working quicker and in case the same thing affects other programs.
Finally, it's a bit of a long shot, but it might be worth trying with the latest beta version of Opus (10.5.2.5, linked in my signature). That has some changes which may affect shell extensions which (potentially) talk to the network, which might include this one. It probably won't make a difference, but the beta has proven stable and it's a quick thing to try, so worth a go in case it saves time.