Check your baseurl value in conf/_config.php. AFAIK the cookie scene hasn't changed at all, so I'd look there first. No trailing slash, and very importantly you should be visiting the url as it is identified. In other words if you have www.blahblah.com that's different than blahblah.com

Oh wait a minute. I get stuck in that cycle sometimes. Do you have multiple installations running with similar baseurls? If you do then the cookies fight it out because there's only one cookie. like blahblah.com is one install, and blahblah.com/foo is another, so they both eat the same cookie. I fix this in one of two ways: my admin passwords are the same on my permanent installations, and for test installs I change the "b2evo_name" parameter in (I always forget this part) conf/_admin or conf/_advanced. That field sets up the cookie name, so now you get a new cookie for a new installation.

Well I'll be dipped, that fixed it. You caught my mistake even when I mis-reported the problem. I have always accessed my site via

http://blog.com/admin/b2edit.php

I changed the links to include the www, and that took care of it. I love it when fixes are this simple.

Thanks EdB!
Chris