"Pages.app" Will Not Open on Mac

My Mac is currently running Pages Version 12.0. I last opened it without problem five days ago. However, when I try to Open it today I get this message: "You can’t open the application “Pages.app” because it is being updated." (There is a little "?" in the Dialog Box but it is a dead link - I get only a blank box. This has never happened to me before in using iMacs for the past 15 years or so.

Is this a common problem? Does Apple refuse to allow users to open apps on their platforms while the apps are being updated?

I would appreciate any help. Thanks