Trying to move from one site to another, I was faced to a problem with the nextgen tables in the database.
First, I used the import function of wordpress, to get back all the content of the migrating site.
I was aware that this wont import the nextgen gallery structure.
So exporting and importing wp_ngg_pictures, wp_ngg_albums, wp_ngg_gallery using phpMyAdmin worked fine.
Every thing was in place, and all work, BUT, not the tags !
All the tags of the images in my galleries come from what I set as keywords in Lightroom, so there are includes in the meta datas of the images files, and are added as tags automatically by NextGen when images are imported in a gallery.
In the galleries (menu "manage gallery"), after the import of the data base, no tags shown.
In the menu "manage image tags", no tags….
If I looked in the data base, in the wp_ngg_pictures meta_data, all the information was there, exif, keywords…
So there is a sort of a link between the gallery and the tags which surely I missed, but I could not find what…
Finally I have found a solution :
1/ Go to Manage gallery
2/ Set bulk action to Import metadata
3/ Select the galleries
After a while (this involve the plugin to read every images) : all the tags are back !
I hope it will be useful for other users.
Reseach on the forum and google did not help me on that subject.