Hi ! I don't know when you added "slug" in NGG gallery table.
I found it in the current code: slug VARCHAR(255) NOT NULL
However in a old WP installation that I just upgraded, I'm not having this column, this provokes SQL errors and it's impossible to add new galleries.
Of course, now I'm using lastest version, but how can I resolve besides from altering table myself ?
The cause of this could have been a "too massive" update ?