Fatal error: Call to undefined function convertsparklingmilies()
is thrown on 404 pages.
It is fixed in Sparkling 1.2 which is currently under review by WordPress.org but you can already download it from here http://wordpress.org/themes/sparkling/developers/
However, it should throw notice not fatal error. You can already go ahead and replace current 404.php file content with updated one from here http://themes.svn.wordpress.org/sparkling/1.2.0/404.php
Otherwise you can wait for automated update which will be available within few days.
Awesome, thanks!