Mmm+ seems to customize context menus in a non-standard way (at least, that's my assumption based on the fact it's supposed to be able to customize context menus of lots of apps which don't provide any API to do so -- someone correct me if I'm wrong as I'm only guessing). So it's not surprising that it doesn't work with Opus, I guess.
There are a couple of old threads on this subject here:
resource.dopus.com/viewtopic.php ... hlight=mmm
resource.dopus.com/viewtopic.php ... hlight=mmm
Opus lets you customize its own menus so if you just want to customize the context menus in Opus you don't need Mmm+, unless I've misunderstood what it does.