After the AdSense updates last week, some publishers experienced problems logging into their AdSense accounts while their AdWords account logins were working correctly. But as of this afternoon, the bug has been fixed, and all publishers should be able to login.
If you were an affected publisher, you should be able to login at http://www.google.com/adsense using your new Google account login information.
It should be noted that only a small number of publishers are affected, as it is being rolled out to accounts, rather than all accounts being asked at once. So if you use the same info for both AdWords and AdSense but haven’t been asked to consolidate your account, you don’t need to worry.