wpmp_the_group_file() on admin pages after upgrading to WordPress Mobile Pack 1.1.9

I just upgraded to WordPress Mobile Pack 1.1.9 and when I try to access admin pages with my mobile phone, I've got this error:

fatal_error: Call to undefined function wpmp_theme_group_file() in [path]/wordpress-mobile-pack/plugins/wpmp_switcher/pages/mobile.php on line 30.