In practically every case, the upload is refused by the server because of restrictive security configurations. The row of the file says why it was refused - a file type Event Gallery does not take, a file which is no image, a file larger than the limit the page names - and a file which fails without a reason is usually one the web server refused before PHP saw it; ask your host for the limits of the web server as well. If the page says that the uploads are paused, your login has expired or the server cannot be reached: log in again in another tab or check the connection, then press Resume - nothing in the list is lost. Please contact your provider. They can fix it. In the meantime, you can use FTP to upload the images to /images/eventgallery/[your folder] and hit the Sync Database button in the main toolbar of the Event Gallery component in the back end.