That isn't the standalone viewer, it's something trying to run ACDSee, which is not part of the default Opus configuration either.
Whose configuration did you import? 
Please tell them to fix this in the config they're giving to people, and preferably also urge them not to encourage people to install a whole custom config over the top of the default one, as it causes problems like this.
To fix the problem, go to Settings > File Types > Recognised Images > Events > Left Double-Click and set it to run Show instead of ACDSee.
A couple of related threads in case the extra info is useful: