I found the problem in function upload_images
located in wp-content/plugins/nextgen-gallery/admin/functions.php
Problem is in $gallery->abspath property. The value is missed suddenly time of time…
I solved the problem by adding the code
$gallery->abspath = WINABSPATH . $gallery->path;
before first occurance
$dest_file = $gallery->abspath . '/' . $filename;
in the function’s code.
May be helpful for you too! ))
