I've renamed a region in my .info file by mistake. After clearing the cache with drush, the block I've attached to that region was disabled. Drush printed the following message:
The block Nivo Slider was assigned to the invalid region slider and has been disabled.
I corrected the false region, but still the block seems to be "disabled" somehow, see picture from structure -> blocks, below.
Already enabled/disabled Nivo Slider Module, cleared cache with drush.