Registered Only Plugin

I’m using this plug in on a private blog and it seems to work ok except…when try to logout it takes me to:
http://mysite.com/wp-admin/post.php
So it takes me to the “post page.” And that’s where I’m able to logout. And when I do that the login page is visiblel but the url says:
http://mysite.com/wp-admin/post.php
again, which means I have to delete “wp-admin/post.php to login again.
***update***
Not I am unable to login in at all. I get this long string in the URI field:

http://mysite.com/wp-login.php/wp-admin/wp-admin/wp-admin/wp-admin/wp-admin/wp-admin/wp-admin/wp-admin/wp-admin/wp-admin/wp-admin/wp-admin/wp-admin/wp-admin/wp-admin/wp-admin/wp-admin/wp-login.php?redirect_to=%2F
Any suggestions on how to fix this?

Thanks!