No Photos & API Invalis

I recently updated the plugin on two of my sites, and both of them are generating “No photos” errors where images should be. When I go to assess the settings and click “Save Changes” I’m given the following error:

“Invalid values, the settings have not been updated
API Key is not valid”

I’ve tried generating a new API key, but I am still given this error. Please help as these are on my clients’ web sites!

https://wordpress.org/plugins/flickr-photostream/