I have 2 Gmail accounts and 1 Yahoo mail account being checked by X-notifier. For a long time now (months), one of my Gmail accounts has been in red. The other 2 email accounts are good.
A long time ago I'd seen this problem but it self-corrected when X-notifier updated. But then it re-appeared (and affected a different Gmail account iirc).
I have uninstalled the app, restarted Chrome, downloaded a fresh copy of X-notifier and imported my files, but the same Gmail account stays in red. The other Gmail account and the Yahoo email account still work fine.
One Gmail account in red
And now, it has somehow fixed itself!
So disregard the above comment.