The same thing is happening to me. I keep getting kicked out to the "please log in again" wp-login page. Once I cleared my cookies and cache, it started dumping me there without any error messages or requests for me to log in, only showing me the standard login screen.
Like with others, I too can access the admin panel by typing in [myblog.com]/wp-admin/. However, I have found that trying to save changes to widgets or any changes under the settings tab dumps me back out to the wp-login page. That issue could be due to the tilde problem, though. (My site is hosted on a [biguniversitydomain.edu]/~[mysite]/ address which has given me problems ever since upgrading to 2.5.0 with redirect loops while performing certain tasks that change between 2.5, 2.5.1, 2.5.2, and now 2.6.)
Looking forward to a full solution!