Same problem, how do you fix it? Change the admin entry in the database or something? Thanks!
Update...nevermind found it. I believe Moshe (sorry if this is the attributed to the wrong user or misspelled) posted it in these forums that the fix action is to:
update admin_user set password=md5('newpassword') where username='admin';
with the appropriate database selected (me, I did it in phpmyadmin)