If you use uBlock (or uBlock origin) and get an error playing videos on YouTube, you might have a filter enabled that causes an interference.
You will then see this error displayed: “An error occurred. Please try again later”. It sometimes is only displayed for a few seconds and then video starts playing.
I recommend you to disable any filters in the Privacy section such as:
From my experience, Fanboy’s Enhanced Tracking List might specifically be causing this issue on YouTube. Once disabled, everything works fine again.