If you created a new application defined facebook tab url there and used app in your fan page to show a tab there, You can see that tab when you are admin. But you cannot see that tab when you are using different email address.
Or you have created a new application and you are trying to view that facebook application from different email address than the email where you created, but you cannot see that application from other email addresses but you can see from that email where you created application.
Don’t worry at all there is no error or bug in facebook, you just have to change setting from your application, Please go to application where you created that, http://www.facebook.com/developers/ then select apps, there select the app edit application and there is an option Sandbox Mode Disable that box, this stops application to show public and tabs to show public related to that app.
Once you disabled your all problems are gone.
