When you delete an Item in the menu you get an error:
Error (ERROR_BAD_PARAMETER) : Class ItemDeleteSingleView not defined in core.ItemDeleteSingle
in C:\xampp\htdocs\gallery23\modules\core\classes\GalleryView.class at line 194 (GalleryCoreApi::error)
in C:\xampp\htdocs\gallery23\modules\core\ItemAdmin.inc at line 123 (GalleryView::loadView)
in C:\xampp\htdocs\gallery23\modules\core\classes\GalleryView.class at line 278 (ItemAdminView::loadTemplate)
in C:\xampp\htdocs\gallery23\main.php at line 449 (GalleryView::doLoadTemplate)
in C:\xampp\htdocs\gallery23\main.php at line 103
in C:\xampp\htdocs\gallery23\main.php at line 88
Solution: Copy the missing files
/modules/core/template/ItemDeleteSingle.tpl
/modules/core/template/ItemDeleteConfirmation.tpl
/modules/core/ItemDeleteConfirmation.inc
and also the corrupt file:
/modules/core/ItemDeleteSingle.inc
from an older release to your directory.
This will solve the problem. Unfortunately there got some code lost.