Q: FCPX 10.2.3 will not open with El Capitan 10.11.5

Do you have older versions of the application on your system?

Russ

What are the complete specs of the system? You only have one version of FCP?

TThat's the absolute minimum system. Let's see the application next. Hold Opt-Cnd as you launch the application and report what happens.

So you don't have 10.2.3. 10.2.1 should open though. Does this appear while holding Opt-Cmd through the launch process. You update your version in the App Store.

Sorry, you should update your version to 10.2.3.

PPlease confirm that you held down Option and Command during the application launch process.

ANd there are no other versions of FCP on your system and any connected drives?