You cannot drag & drop from a normal application to an elevated application. (This is not specific Opus; it's how UAC works.)
Instead of running Opus elevated via UAC, run Opus normally and use Opus's built-in UAC support and, if you want to reduce the number of UAC prompts you see, Opus's Admin Mode feature (which elevates all operations performed in a window with just a single UAC prompt).
See the FAQ for more information: Why NOT to run Opus as Administrator in Vista / Windows 7