Irritating behaviour

Thank you for that reply. Under Mission Control, no Active Corners are set up, and in fact my 'irritating behaviour' happens anywhere along the top edge of the screen. I attach a screen-shot of the Mission Control (System Preferences) window.n.

Thank you very much. I tried starting in Safe Mode, but my Mac would not comply. That's another story, I suppose. But in Syst.Prefs/Mission Control I found two secondary shortcuts for starting and stopping the screen-saver, so I disabled those — and the problem is solved! Thank you again.

This is getting very confusing! Today it was behaving irritatingly. I then had occasion to shut the computer down and restart it — no change. However, later in the day I restarted the computer yet again, and this time the irritating behaviour had gone.

I am logged. in as Admin., and I haven't got any cleaning or optimizing apps that would start up without my starting them.

Thanks. very much for continuing to engage with this — now not only irritating behaviour, but inconsistent, too.

Thanks very much yet once more. I shall wait and see how the Mac behaves in the next few days. At the moment it is behaving well. If it misbehaves again, I shall take your advice and re-instal Mojave. I can't upgrade because Photoshop, installed on my Mac, would then misbehave; and I don't do enough photographic work to make it worth my while to subscribe to Photoshop online. Caught in the middle!

Well, things got worse. A new phenomenon appeared: all folders and apps are locked up immediately upon starting up. When I restarted the Mac repeatedly, two times out of three — perhaps even 3 times out of 4 — everything was locked up like that. Just occasionally folders and apps were accessible and working. So in the end I took your advice and downloaded and installed a new copy of Mojave over my old one.

I am holding my breath: folders and apps are working normally and the 'irritating behaviour' is not manifesting itself. Will this happy state of affairs last? Time will tell.

Time did indeed tell. The faults — both the grey screen and folders and apps being locked on start-up — reappeared. So reinstalling Mojave had not done the trick. Then it dawned on me: I deleted AccessMenubarApps.app, and I do believe both problems really are now cured. I hope this saga may be of use to others, too.

Oh dear! That was fine yesterday. Today, my 'irritating behaviour' is back just as before. And I cannot un-tick some of the items in Mission Control.