Hi, (I'll get straight to the problem) as you can probably guess from the title,
Fatal error: Class 'nggTags' not found in wp-content\plugins\nextgen-nivoslider\
is the error I get when trying to use the widget on a widget area I made.
The widget has 'slider' set in the "Only display images tagged as:" text field, and that is the slug of the tag I made. I made sure to tag all posts with it.
I've tried re-installing the plugin, no hope.