Question: How do I fix "This action could not be completed. Try again."?
I receive the message "This action could not be completed. Try again." when attempting to log into the Apple App Store from my 2017 15" MacBook Pro with High Sierra v. 10.13.3. The username and password are good, as I can use them to access other Apple sites, e.g., "iCloud", and "Manage Your Apple ID". I can log into the App Store from a different MacBook Pro, but not from the computer in question. My wife can log into the App Store from the other computer, but not from the one with the problem. This leads me to the conclusion that the problem is with my computer, not my account.
To this MacBook Pro I transferred many files – Applications, Library, Desktop, Downloads, etc. – from my old MacBook Pro. I suspect I copied a file (or files) that is causing the problem, but I don't know which file. How can I resolve this issue?