Index: modules/system/system.admin.inc
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.admin.inc,v
retrieving revision 1.281
diff -u -p -r1.281 system.admin.inc
--- modules/system/system.admin.inc	16 May 2010 20:08:38 -0000	1.281
+++ modules/system/system.admin.inc	17 May 2010 19:51:28 -0000
@@ -1217,7 +1217,9 @@ function system_modules_submit($form, &$
       if (!drupal_check_module($module)) {
         unset($new_modules[$key]);
       }
-      $sort[$module] = $files[$module]->sort;
+      else {
+        $sort[$module] = $files[$module]->sort;
+      }
     }
     array_multisort($sort, SORT_DESC, $new_modules);
     module_enable($new_modules, FALSE);