It looks like the source of the error is the Word login checker. This may happen when WP logs you out while you still have MT open. Refreshing the page and logging back in should normally solve that. But if not, there may be another issue at play.
Would you mind sending me access for the affected site via our secure contact form so I can troubleshoot? You can use this handy plugin to provide access temporarily without sharing login details: https://en-gb.wordpress.org/plugins/temporary-login-without-password/
Or just create a temporary user account with Administrator access, which you can delete afterwards.
You’re welcome. It made have simply been the upgrade process that fixed things for you as the last update addressed a different issue. If it crops up again please let me know.
