If you install Pathauto 7.x-1.2 in the last Drupal stable version (7.21) and try to define some new url patterns for your content type’s (under ?q=admin/config/search/path/patterns or Administration > Search and metadata > Url aliases > Pattern tab) it is likely that an empty “ugly” page shows up…
This was driving me nuts but I finally found how to make it work.
Scenario:
Drupal 7.21
Token 7.x-1.5
Pathauto 7.x-1.2
Admin theme: Seven
The fix
It seems that Seven theme is responsible for this. This theme has some issues with js/jQuery and won’t show (out of the box) the Pathauto pattern’s.
To fix it, just go to Appearance, scroll down to the bottom of the page and select “Bartik” or “Garland” instead of “Seven“.
Now save, and reload ?q=admin/config/search/path/patterns. The pattern tab info should be nicely displayed now.
If it works, you can try to activate Seven theme for admin again. In my case, it worked.