In Xcode 8.0, 2 errors appear on General > Targets > Signing page
The operation couldn’t be completed. Unable to log in with account ‘account email address’. An unexpected failure occurred while logging in (Underlying error code 1100).
No signing certificate "iOS Development" found No "iOS Development" signing certificate matching team ID “TEAMID” with a private key was found.
In Xcode, open the menu Xcode > Preferences
In Apple IDs, select the relevant Apple ID
You should see a error “Your session has expired. Please log in.”
Click Sign In Again…
Enter your Apple ID password and click Sign In
If there are any subsequent issues with the certificate still not being found, close and reopen Xcode to ensure the change takes effect.