It's probably best to start a new thread and describe exactly what's happening and what you're tried, rather than resurrect a 15 year old thread. 
As a guess, make sure Opus has not been run as administrator: Why NOT to run Opus as Administrator under UAC
(Although, if it was running as admin, you should see a warning about that in the Explorer Replacement page in Preferences.)
Which folders have are you double-clicking? What happens instead? Does Explorer open, or nothing, or something else?