Opus comes with several Opus viewer plugins which can go wrong in certain situations (e.g. with certain files which confuse them or components which they dependon). Disabling Shell Image Extraction as well as the Movie plugin in Opus is a good first bet.
Following the steps in this FAQ entry is the way to find out what is going wrong:
[Crash, exit or high CPU when viewing certain directories)
Once you work out which file or plugin is causing the problem it can be looked at and hopefully fixed (and disabled in the meantime).
How large are we talking?