On Thursday we reported that some AdSense publishers were having issues logging in. We thought it had to do with publishers who had a manual review on their account, but we were not a 100% sure of that.
Publishers unable to log in
Details: We've received reports that some publishers are having difficulty accessing their AdSense accounts, and are seeing that the login page reloads even after having cleared the cache and enabled cookies. Our engineers have been notified and are investigating this issue to resolve it as soon as possible. We'll keep you updated with any details as we receive them, and we apologize for any inconvenience caused.
The thing is, this is still an issue for many publishers even about four days later. There is currently no estimated time for when the fix will be in place.
Forum discussion at Google AdSense Help.