Are you definitely using Opus Pro if you check via Help > About Directory Opus? (The Admin Mode button would only appear in Pro, although general UAC support should work in both Pro and Light, e.g. when copying to folders that trigger a UAC prompt that should work in both versions.)
Check that compatibility mode hasn't been turned on for dopus.exe. e.g. If Windows is telling Opus that it is running on Windows XP then all the UAC support would be disabled.
Re-running the installer over the top of the existing installation, then rebooting, is also worth a try, in case the problem is one of the DLLs involved in UAC support has had its registry settings damaged.