Page Returns 404 error when I try to upload a photos

I am creating a Gallery and it takes me to the upload page. Once I choose the the photographs its redirecting to 404 page not found with the following URL

wp-admin/admin.php?page=nggallery-add-gallery&skipjs[0]=https://www.xxxx.com/wp-content/plugins/nextgen-gallery/admin/js/ngg.progressbar.js?ver=2.0.1

Kindly assist to fix

https://www.ads-software.com/extend/plugins/nextgen-gallery/