Im am using movie studio 18. Even though I had this same issue with movie studio 14. I bought 18 in hopes this issue would have been fixed...

I click the upload arrow in the top left corner and select share to youtube, it will pull up a small browser window with a log in screen. After i log in to my google account, an error appears saying there was some issue blocking me from getting access. From my experience it seems lile the browser window that movie studio intially pulls up is way out of date. Now ive tried to navigate through that window and update the browser but it crashes eveytime after that.