In Camtasia when you click on Share to YouTube, you type in your email and click Next but it does not advance and then Next becomes grayed out.
This behavior can happen with two factor authentication enabled on your google account. One workaround would be to disable two factor authentication. Another workaround would be to produce an MP4 to your local hard drive and then manually upload to YouTube. Some users have reported disabling two factor authentication, rendering a video to Google Drive and then re-enabling two factor authentication will make it work for future uploads to Google Drive.