Same problem. Updated the plugin to the latest, update failed and all existing galleries gone. Plugin no longer appears in list and reinstall fails:
Downloading install package from http://downloads.wordpress.org/plugin/nextgen-gallery.zip…
Unpacking the package…
Installing the plugin…
Destination folder already exists. C:/wordpress/wp-content/plugins/nextgen-gallery/
Plugin install failed.
Gallery 1.9.12
Wordpress 3.5.1
Like JEBERLECO I’d rather not have to recreate all the galleries 🙂
Site is a self hosted intranet, not publicly accessible
