Hi, I just discovered the issue yesterday and the solution today so I thought I'd write in if it's any help.
My blog is non-beta, I haven't switched over yet. The blogs I wanted to comment in suddenly began rejecting my comments saying "Could not log you in. Double check or try later." Below it says 'No Google account? Sign up here' and 'You can also use your blogger account" but that is not a link. Then today, it struck me that I could try using my gmail ID - and it worked. But I still need to use my Blogger ID and password to get into blogger - the gmail ID didn't work.
This Post was written by Sra from When My Soup Came Alive.