I’m having a similar issue.
I uninstalled 2.5 and installed 2.6.2. Now I am unable to access my admin page/Dashboard. I can see the blog post, but nothing else.
…./wordpress/index.php — shows blog post
…./wordpress/wp-admin — blank screen
from blog post, I can select “log in” which brings me to the WordPress login page
…./wordpress/wp-login.php
this returns “ERROR: Invalid username.”
