I’m having the exact same problem….began just about 3 days ago completely randomly. I hadn’t made any changes to WordPress or the site. I cannot access the WP login screen via https://www.mydomain.org/wp-admin it just keeps giving the pop-up window netforest mentions above. Have cleared caches/cookies on all browsers, yet nothing.
The site is still up and working fine, just cannot login.
Anyone know what going on??
