If two step verification is turned on for your google account that can potentially block the upload as well.
- Try turning off two step verification on your google account
- Make an app specific password for Camtasia from your google account
You can also export to your hard drive with Share > Export to create an mp4 video file and manually upload that file to YouTube in your web browser.
Camtasia for Mac 2 accepts either Google or YouTube credentials for login.