Disable whatever plugin or automation you have running when you open files.
Not really sure how to do that since I've never touched/messed with any plugins or automations.
Most likely something you installed has added an event script for event "open".
Go to File -> Scripts -> Script Event Manager and disable everything you find there.
At the top of the box theres an "Enable Events to Run Scripts/Actions:" and it is unchecked but it is still saying "Command not "set"". I'm using CS6 if that matters at all. Thanks for you help BTW.
You are running some sort of automation when you open files - because that error message comes from automation (actions, scripts or plugins) that are trying to target something that isn't there.
Event Scripts was the obvious choice.
Automation plugins, or Flash Panels are the next most obvious -- try disabling all third party plugins and Flash Panels.
The error might come from Generator, if you have the latest Photoshop CC.
I'm also having this problem. Sorry to cross-post and bump an old thread, but as I don't seem to be getting anywhere with this thread: https://forums.adobe.com/thread/2077129 (despite their best efforts), it would be great to get your ear, Chris. I've tried shift-launching Photoshop to disable plugins, made sure 'Enable Events to Run Scripts/Actions' is unchecked, and made sure Generator is disabled, but I still have this problem with some files.
It's happening on three different Macs, but opens fine on a Windows machine that I've installed a trial on.