Comment 1 for bug 308256

There might be a clash because 'admin' is already an existing page.

However ... do you really need to move the login block this way?

If you just want the login form to occur on a single page in the content area, just use the page with path 'user' or 'user/login', and hide the 'User Login' block completely.

For example, ProsePoint (with the default theme and settings) comes with a link in the top right called 'Login'. You can just rename that menu item to 'Admin'.