Please, enter correct Facebook API settings


I've got an issue with this plugin.

Buddypress/multisite, all up to date.

It worked for a while, then started failing with no obvious reason - no change to the plugin or app (loads to the website & lots of plugins installed)

I've triple checked the details on FB, and all the URLs are right.

I can get into the plugin through network admin, but cannot change the settings as I cannot get past the first tab.

On the home site I have the plugin activated but canot see any settings on there - not sure if I should.