I tried to disable nivo slider and uninstall it from plugin list, but when I re-install and re-enable it I see the same slider I created before.
So I tried to use this plugin https://wordpress.org/plugins/wordpress-reset/ to totally reset wordpress. The old slider was gone, but the issue didn’t.
So i tried to install Nivo slider 2.2 from a previous startupwp version. Now it works.
My question now is: what happened and why?
note: resetting wordpress has reset also your credentials, ask if you need them.