Multisite with Subfolder Mapping

Hi guys!

I have installed the Nextgen Gallery Plugin on a Multisite with 2 Sites (https://69.195.124.113/~villaghi/) and have created 3 galleries on the first website (en version).

The problem is with the second site (greek version) where I do not even get the gallery settings. When I click ‘other options’, the plugin returns the following: “Exception thrown – Please specify the primary key for ejd_2_ngg_pictures”

I have added the RewriteRule ^wp-content/blogs\.dir/([0-9]+/)(.*) wp-content/$2 [L]
command in my .htaccess (I read it in another discussion) but still nothing.

Any ideas on how I can get the plugin work in the second website?

Thank you.

https://www.ads-software.com/plugins/nextgen-gallery/