Why is Views Nivo Slideshow block only displaying to logged in users?
I have some problems with blocks before and I always check the following, it has solved my problems so far.


Check your block permission.
Verify the block is assigned to a valid region setting in your template.
Rebuild the node permissions in admin/reports/status. Before doing this, backup your database and clear the cache.
Verify the access permission used from the view is view published content.


When I am working with views, I make sure the theme developer module is not enabled. I disable it, and then I clear the cache.