I am sorry, all look like you did some update.
Please check: for continue all work good you can't do update Pro Joomla Photo Gallery to Free Joomla Photo Gallery
If you install (not update) Joomla Gallery, Please uninstall it and install gallery again. For check appear error or not.
If you do update, Please give more details from which version you do update.
For fix error please in phpMyAdmin run:
ALTER TABLE `#__os_gallery_connect` ADD `ordering` INT(11) NOT NULL DEFAULT '0' AFTER `fk_gal_img_id`;
where "#_" replace to your prefix.