That's OK, I'll wait.
Mine runs High Sierra, the latest version of it, 10.13.6.
That's odd. It should work. I think it has something to do with getting caught by the sandbox, and stuck in the 'Verifying' step.
I haven't done all the troubleshooting I can do. There's a workaround in Terminal for this sort of thing, usually. I'll have to check the Console, for errors and then look it up. Normally Ctrl-Click fixes this sort of problem. I haven't had this kind of trouble with a file since I was running OS 10.11 on another computer. That required something a little more involved. I'm sure it's all down to the system security software.
--RB