After installation WP 5.02 error on NextGen

After installation Gutenberg I get in edit-mode errormessage about NextGen:
Warning: file_get_contents(https://WWW.herensocieteitamicitia.com/amicitia/wordpress/wp-content/plugins/nextgen-gallery/products/photocrati_nextgen/modules/attach_to_post/static/ngg_attach_to_post_tinymce_plugin .min.css): failed to open stream: HTTP request failed! HTIP/1.1401 Authorization Required in home/vhosts/herensocieteitamic itia.com/httpdocs/am icitia/wordpress/wp-content/plugins/gutenberg/ lib/client-assets.php on line 1225

I see on file line 1225 : (see arrows)
if ( $editor_styles && current_theme_supports( ‘editor-styles’ ) ) {
foreach ( $editor_styles as $style ) {
if ( filter_var( $style, FILTER_VALIDATE_URL ) ) {
$styles[] = array(
‘css’ => file_get_contents( $style ), <<<<<<
);
} else {
$file = get_theme_file_path( $style );
if ( file_exists( $file ) ) {
$styles[] = array(
‘css’ => file_get_contents( $file ),
‘baseURL’ => get_theme_file_uri( $style ),

If I deactivate NextGen problem is over.
Please advice.

Wim.

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