Get error 500 when trying to edit menu item - Joomla! Forum - community, help and support

hi, seems since recent update joomla 2.5.7 when trying edit menu item:

500 - error has occurred.
error loading form file

return control panel

there no clues in error log. switching on error reporting not produce anything.

debug gives me this:

call stack
# function location
1 jadministrator->dispatch() /var/www/vhosts/xxxxxxxxxx/xxxxx/administrator/index.php:46
2 jcomponenthelper::rendercomponent() /var/www/vhosts/xxxxxxxxxx/xxxxx/administrator/includes/application.php:153
3 jcomponenthelper::executecomponent() /var/www/vhosts/xxxxxxxxxx/xxxxx/libraries/joomla/application/component/helper.php:348
4 require_once() /var/www/vhosts/xxxxxxxxxx/xxxxx/libraries/joomla/application/component/helper.php:380
5 jcontroller->execute() /var/www/vhosts/xxxxxxxxxx/xxxxx/administrator/components/com_menus/menus.php:18
6 menuscontroller->display() /var/www/vhosts/xxxxxxxxxx/xxxxx/libraries/joomla/application/component/controller.php:761
7 jcontroller->display() /var/www/vhosts/xxxxxxxxxx/xxxxx/administrator/components/com_menus/controller.php:58
8 menusviewitem->display() /var/www/vhosts/xxxxxxxxxx/xxxxx/libraries/joomla/application/component/controller.php:722
9 jerror::raiseerror() /var/www/vhosts/xxxxxxxxxx/xxxxx/administrator/components/com_menus/views/item/view.html.php:35
10 jerror::raise() /var/www/vhosts/xxxxxxxxxx/xxxxx/libraries/joomla/error/error.php:251

i've tried uploading administrator/components/com_menu folder t afresh joomla 2.5.7 download, ti did not make difference.
someone suggested clearing cookies , trying different browser, not make sense anyway, ja, tried , did not work.

login back-end/ extensions manager/ tab database/ click fix button