Try making some change to your admin in the Users tab. I think it may be related to this problem:
http://ww.wp.xz.cn/support/topic/106413?replies=8
I think you can make any change to the admin user, and it will fix this problem.
I did it by checking the checkbox next to my admin user on the main Users page, selecting “Set the Role of checked users to: Administrator”, and clicking “Bulk Update”.
The underlying problem seems to be that the “user_level” field in the database does not exist for the admin user, but changing the user causes it to be created. I suspect user_level might be a deprecated database field and so it’s not always populated.
