I`ve got the same problem. Suddenly the basic thumbnail gallery does not show any more. "No images were found" on all pages with galleries.
Albums are fine.
Images are all accessible from Gallery/Manage Galleries.
This is what I tried so far:
use old and new shortcodes and image browser - no change
disabled all other plugins - no change
changed theme to twenty-thirteen - no change
renamed folder plugins/nextgen-gallery to plugins/nextgen-gallery.old and copied fresh Nextgen Gallery files by ftp onto server (reinstall plugin)- no change
Not only do existing galleries no longer show up on pages, adding a gallery to a new page just shows red triangle.
This happens with NEXTGEN Basic Thumbnails, NEXTGEN Basic Slideshow, NEXTGEN Image Browser
I can however choose a single image from any Gallery via "Media"/"NEXTGEN Gallery" -> choose gallery -> show -> import image
which then shows on a page.
Draft or Published, no difference.
DB Repair done with no errors.
Here`s one of the affected pages of my blog:
WP is 3.6.1
NEXTGEN Gallery Plugin is 2.0.40
I did not update WP because I doubt it would help. In fact I guess there will be more problems if I do...
It used to work fine just days ago. No clue what might have happened.
Hope someone can help!