Arrisje, downgrading did the trick. Thank you very much.
I now understand why it did not work. The problem with the new version of Nextgen is that you now select your template from a dropdownlist in Display Galleries/Customize the display settings/Template.
And there’s no option ‘gallery-customlinks.php’. And you cannot manually add the shortcode template=customlinks to the page where you inserted the gallery (so the code looked like this [nggallery id=x template=customlinks] ). Without this, you’ll never get the tutorial working.
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I also added some extra code in de gallery-custom.php to open a new window when clicking on a thumbnail. My code (stap 7 in the tutorial) now looks like this:
<div id="ngg-image-<?php echo $image->pid ?>" class="ngg-gallery-thumbnail-box" <?php echo $image->style ?> >
<div class="ngg-gallery-thumbnail" >
<a target=\"_blank\" href="<?php echo $image->ngg_custom_fields["Link nieuw venster"]; ?>" title="<?php echo $image->description ?>" <?php echo $image->thumbcode ?> ><img title="<?php echo $image->alttext ?>" alt="<?php echo $image->alttext ?>" src="<?php echo $image->thumbnailURL ?>" border="0" <?php echo $image->size ?> /></a>
</div>
</div>
So I added to the link the code target=”\_blank\”
