If the items are added okay but don't do anything when selected then I think you will have to ask the ShelltoysXP to describe what happens when they are selected. Perhaps they are triggering some kind of message which Explorer understands but Opus doesn't know about and ignore.
If it opens things in a new Explorer window then it is probably launching the folders incorrectly.
My bet is that it is either calling Explorer.exe directly or using the ShellExecute API but incorrectly passing "open" for the verb instead of leaving the verb null to pick up the default action. (See here for why the verb should be null and not "open".)