Update March 17:
Most people are reporting the error is no longer occurring. If you're still seeing it, please use the workarounds below. We'll continue monitoring the issue until it's history. :)
Update March 14:
According to this comment in an ABP forum post, a recent change in the YouTube player code accidentally broke video playback when an ad blocker is in use. According to another comment, it may be related to a new ad delivery system YouTube started rolling out a few months ago. And according to still another post on Reddit, there is a second workaround that's successful for the majority of people who are trying it.
Go to Google Ad settings for the account you use with YouTube and opt out of interest-based ads on both Google sites and elsewhere. Then install the IBA Opt-Out extension.
Browse to Google.com, click the Google apps button, and select My Account.
Under Personal info & privacy click Ads settings.
Click Manage ad settings.
On the Control your Google ads page, scroll down and turn off Ads based on your interests.
Click SWITCH OFF when prompted to confirm, then click CONTROL SIGNED OUT ADS.
Turn off Ads based on your interests on websites beyond google.com.
Click SWITCH OFF when prompted to confirm, then click I'M DONE.
- Install the IBA Opt-Out extension by Google.
If that doesn't help. try Workaround #1 below!
Since March 9, YouTube videos have started showing the message "An error occurred. Please try again later" and a blank screen for several seconds. After that, the video plays.
We found several reports about this on various YouTube, Reddit, and EasyList forums. The error only affects videos with ads. It's happening with all the major ad blockers in both Firefox and Chrome, with and without an ad blocker running. It seems to be related to a YouTube update released in the past couple of days rather than an issue specifically with any particular ad blocker or filter list.
The only consistently successful workaround we've seen reported is to watch ad-supported videos while logged out of Chrome and YouTube. Alternatively, just wait a few seconds and the video will play normally.
We'll post an update when we know more!