Windows XP only:
A recent Microsoft Windows Update, KB921398, introduced a problem wherein double-clicks or right-clicks on some items on the Desktop are ignored in Opus (that is, if you are viewing the Desktop folder in an Opus Lister).
The problem has been seen to affect the My Documents folder, ZIP files and possibly normal folders.
The problem appears to have been caused by KB921398, which was part of the recent round of Microsoft updates (security bulletin MS06-045).
We have no idea why this update affected Opus in this way, nor do we have any idea how to solve the problem at the moment. All we can suggest is to uninstall this update. Note that the update is only rated as "important", not "critical" - so we believe uninstalling it is a viable option, at least until we have a better solution.
Note that this problem affects almost all programs and not just Opus. If you are experiencing the problem you should also notice the same issues with right-clicking .zip files on the Desktop when using the standard File -> Open in any other program. It is that general problem which is affecting the Desktop folder (and possibly others) within Opus for Windows XP users with KB921398 installed.