The editor has encountered an unexpected error

I just installed the plugin and got this message in the User Post Gallery window after pressing Add UPG-Post

Here’s the error code:

Error: An error occurred while running 'mapSelect': Cannot read property 'ngg_post_thumbnail' of undefined
The error may be correlated with this previous error:
TypeError: Cannot read property 'ngg_post_thumbnail' of undefined
    at https://localhost/testsite/wp-content/plugins/nextgen-gallery/products/photocrati_nextgen/modules/nextgen_block/static/build/post-thumbnail.min.js?ver=3.3.5:1:13830
    at Object.current (https://localhost/testsite/wp-includes/js/dist/data.min.js?ver=e80048e7b309581a40e44b8bd8aaba41:2:24934)
    at e (https://localhost/testsite/wp-includes/js/dist/data.min.js?ver=e80048e7b309581a40e44b8bd8aaba41:2:24561)
    at https://localhost/testsite/wp-includes/js/dist/data.min.js?ver=e80048e7b309581a40e44b8bd8aaba41:2:24670
    at Vb (https://localhost/testsite/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.9.0:104:431)
    at Ti (https://localhost/testsite/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.9.0:148:85)
    at unstable_runWithPriority (https://localhost/testsite/wp-includes/js/dist/vendor/react.min.js?ver=16.9.0:26:340)
    at Ma (https://localhost/testsite/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.9.0:52:280)
    at Ia (https://localhost/testsite/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.9.0:140:407)
    at ze (https://localhost/testsite/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.9.0:118:14)

Original stack trace:
    at Ge (https://localhost/testsite/wp-includes/js/dist/data.min.js?ver=e80048e7b309581a40e44b8bd8aaba41:2:24353)
    at https://localhost/testsite/wp-includes/js/dist/data.min.js?ver=e80048e7b309581a40e44b8bd8aaba41:2:24909
    at je (https://localhost/testsite/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.9.0:78:476)
    at qe (https://localhost/testsite/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.9.0:89:115)
    at ph (https://localhost/testsite/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.9.0:216:489)
    at lh (https://localhost/testsite/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.9.0:126:409)
    at O (https://localhost/testsite/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.9.0:121:71)
    at ze (https://localhost/testsite/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.9.0:118:14)
    at https://localhost/testsite/wp-includes/js/dist/vendor/react-dom.min.js?ver=16.9.0:53:49
    at unstable_runWithPriority (https://localhost/testsite/wp-includes/js/dist/vendor/react.min.js?ver=16.9.0:26:340)