ERROR page? I have had one for over 14 months.
It's really easy to access IMDb with an unintended account (Google, Amazon, Facebook).
The feature is still easily found in the Help text, and I don't remember an announcement that it's been disabled, but I've never had that feature.
If you're sure you logged in under the account that has Scorecard authorized, you might need to Contact the Help Desk.
If you have IMDb Pro, there is a way to set your first Demo Reel. Have you read this in the help topics? It requires that you have at least two....
Can I change the order of videos/demo reels on my page so that a specific reel appears first?
You can designate a primary demo reel that will be shown first in the list of related videos on your IMDb page. To designate your primary demo reel, upload more than one demo reel, then select the "Set as Primary Demo Reel" on the Your Videos page.
It says you did figure it out in you post, but if not I posted this for you, just in case.