How to remove Error message

I am getting this error message –

Recently an error occurred while creating the CSS / JS minify cache: Unable to cache remote file: "http://macrodiver.com/wp-content/plugins/nextgen-gallery/products/photocrati_nextgen/modules/nextgen_gallery_display/static/fontawesome/font-awesome.css?68e346".

It’s coming from the w3 total cache but I can’t get rid of it and I do not have nextgen installed as a plugin – it’s been deleted.

I’ve cleared caches, disabled and then enabled minify settings, deactivated and reactivated the total cache plugin but i keep getting the same message.

any suggestions that doesn’t involve me having to delete total cache and start all over??

thanks