NextGEN Gallery plugin breaks visual editor

Hi,

I have a problem with the NextGEN Gallery Plugin: when I enable the plugin, the visual editor is broken: it is not possible to type anything in the editor. Here is a screenshot: https://www.dropbox.com/s/wxz1nl83xr0u7ei/broken_editor.jpg?dl=0

My WordPress installation runs on Debian testing. I use the prepackaged version of WordPress (4.7+dfsg-2).

I use a multi site installation with the following file layout:

Wordpress content is under /srv/www/wp-content/www.michael-thaler.com

The following files are in the directory:

drwxr-xr-x 2 root www-data 4096 Jan 2 18:33 blogs.dir
lrwxrwxrwx 1 root root 39 Jan 2 18:34 languages -> /var/lib/wordpress/wp-content/languages
drwxr-xr-x 3 www-data www-data 4096 Jan 3 07:15 ngg
lrwxrwxrwx 1 root root 37 Jan 2 18:36 plugins -> /var/lib/wordpress/wp-content/plugins
lrwxrwxrwx 1 root root 37 Jan 2 18:36 themes -> /var/lib/wordpress/wp-content/themes/
drwxr-xr-x 2 www-data www-data 4096 Jan 2 18:36 upgrade
drwxr-xr-x 3 www-data www-data 4096 Jan 2 19:03 uploads

The contents of /var/lib/wordpress/wp-content are:

-rw-r–r– 1 www-data www-data 28 Dec 6 20:58 index.php
drwxrwxr-x 4 www-data www-data 12288 Aug 1 19:54 languages
drwxrwxr-x 19 www-data www-data 4096 Jan 4 06:35 plugins
drwxrwxr-x 5 root www-data 4096 Jan 2 18:44 themes
drwxrwxr-x 3 root www-data 4096 Jan 11 2016 uploads

I use the following Apache configuration file:

NameVirtualHost *:80

<VirtualHost *:80>
UseCanonicalName Off
VirtualDocumentRoot /usr/share/wordpress
Alias /wp-content /var/lib/wordpress/wp-content
Options All

# wp-content in /srv/www/wp-content/$0
RewriteEngine On
RewriteRule ^/wp-content/(.*)$ /srv/www/wp-content/%{HTTP_HOST}/$1

<Directory /usr/share/wordpress>
AllowOverride All
</Directory>
</VirtualHost>

Apache version is 2.4.23-8

I found some errors in the Apache log:

[Tue Jan 03 07:15:40.045018 2017] [:error] [pid 15134] [client 46.244.165.95:45
612] WordPress database error Table ‘michaelthaler.wp_ngg_gallery’ doesn’t exis
t for query ALTER TABLE wp_ngg_gallery ADD COLUMN gid BIGINT made by requir
e_once(‘wp-admin/admin.php’), require_once(‘wp-load.php’), require_once(‘wp-con
fig.php’), require_once(‘wp-settings.php’), include_once(‘/var/lib/wordpress/wp
-content/plugins/nextgen-gallery/nggallery.php’), C_NextGEN_Bootstrap->__constr
uct, C_NextGEN_Bootstrap->_load_pope, C_Component_Registry->initialize_all_modu
les, C_Component_Registry->initialize_module, M_NextGen_Admin->initialize, M_Ne
xtGen_Admin->init_wizards, C_Gallery_Mapper::get_instance, ExtensibleObject->__
construct, ReflectionMethod->invokeArgs, C_Gallery_Mapper->initialize, C_Custom
Table_DataMapper_Driver->initialize, C_Gallery_Mapper->migrate, ExtensibleObjec
t->__call, ExtensibleObject->_exec_cached_method, ReflectionMethod->invokeArgs,
C_CustomTable_DataMapper_Driver_Mixin->migrate, C_Gallery_Mapper->_add_column,
ExtensibleObject->__call, ExtensibleObject->_exec_cached_method, ReflectionMet
hod->invokeArgs, Mixin_NextGen_Table_Extras->_add_column, Mixin->call_parent, E
xtensibleObject->call_method, ExtensibleObject->__call, ExtensibleObject->_exec
_cached_method, ReflectionMethod->invokeArgs, C_CustomTable_DataMapper_Driver_M
ixin->_add_column, referer: https://www.michael-thaler.com/wp-admin/plugins.php
[Tue Jan 03 07:15:40.045540 2017] [:error] [pid 15134] [client 46.244.165.95:45
612] WordPress database error Table ‘michaelthaler.wp_ngg_gallery’ doesn’t exis
t for query SHOW COLUMNS FROM wp_ngg_gallery made by require_once(‘wp-admin/a
dmin.php’), require_once(‘wp-load.php’), require_once(‘wp-config.php’), require
_once(‘wp-settings.php’), include_once(‘/var/lib/wordpress/wp-content/plugins/n
extgen-gallery/nggallery.php’), C_NextGEN_Bootstrap->__construct, C_NextGEN_Boo
tstrap->_load_pope, C_Component_Registry->initialize_all_modules, C_Component_Registry->initialize_module, M_NextGen_Admin->initialize, M_NextGen_Admin->init_wizards, C_Gallery_Mapper::get_instance, ExtensibleObject->__construct, ReflectionMethod->invokeArgs, C_Gallery_Mapper->initialize, C_CustomTable_DataMapper_Driver->initialize, C_Gallery_Mapper->migrate, ExtensibleObject->__call, ExtensibleObject->_exec_cached_method, ReflectionMethod->invokeArgs, C_CustomTable_DataMapper_Driver_Mixin->migrate, C_Gallery_Mapper->_add_column, ExtensibleObject->__call, ExtensibleObject->_exec_cached_method, ReflectionMethod->invokeArgs, Mixin_NextGen_Table_Extras->_add_column, Mixin->call_parent, ExtensibleObject->call_method, ExtensibleObject->__call, ExtensibleObject->_exec_cached_method, ReflectionMethod->invokeArgs, C_CustomTable_DataMapper_Driver_Mixin->_add_column, C_DataMapper_Driver_Base->update_columns_cache, referer: https://www.michael-thaler.com/wp-admin/plugins.php

[Tue Jan 03 07:15:40.047220 2017] [:error] [pid 15134] [client 46.244.165.95:45
612] WordPress database error Table ‘michaelthaler.wp_ngg_gallery’ doesn’t exis
t for query SHOW COLUMNS FROM wp_ngg_gallery made by require_once(‘wp-admin/a
dmin.php’), require_once(‘wp-load.php’), require_once(‘wp-config.php’), require
_once(‘wp-settings.php’), include_once(‘/var/lib/wordpress/wp-content/plugins/n
extgen-gallery/nggallery.php’), C_NextGEN_Bootstrap->__construct, C_NextGEN_Boo
tstrap->_load_pope, C_Component_Registry->initialize_all_modules, C_Component_R
egistry->initialize_module, M_NextGen_Admin->initialize, M_NextGen_Admin->init_
wizards, C_Gallery_Mapper::get_instance, ExtensibleObject->__construct, Reflect
ionMethod->invokeArgs, C_Gallery_Mapper->initialize, C_CustomTable_DataMapper_D
river->initialize, C_Gallery_Mapper->migrate, ExtensibleObject->__call, Extensi
bleObject->_exec_cached_method, ReflectionMethod->invokeArgs, C_CustomTable_Dat
aMapper_Driver_Mixin->migrate, C_Gallery_Mapper->_add_column, ExtensibleObject-
>__call, ExtensibleObject->_exec_cached_method, ReflectionMethod->invokeArgs, M
ixin_NextGen_Table_Extras->_add_column, Mixin->call_parent, ExtensibleObject->c
all_method, ExtensibleObject->__call, ExtensibleObject->_exec_cached_method, Re
flectionMethod->invokeArgs, C_CustomTable_DataMapper_Driver_Mixin->_add_column,
C_DataMapper_Driver_Base->update_columns_cache, referer: https://www.michael-thaler.com/wp-admin/plugins.php

There are more error messages like this

I tried to disable all plugins except the NextGEN Gallery plugin and changed the Theme to Twenty-Sixteen, but nothing helped.

I set up the blog a few days ago, it is a new installation (I have other blogs running on the same WordPress, but they are not using NextGEN Gallery)

How can I fix this?

Thanks,
Michael