Adblock is an tiny extension which blocks ads from websites. Hence it is used by millions of people worldwide. Some of the Internet users are reporting YouTube is displaying “An error has occured” while those users attempt to view videos on the website while using Adblock.
When user log out from there youtube account and attempt to view the videos again, they can access the videos. Which caused Adblock community members to suspect Google is flagging the accounts that use adblockers.
Youtube is one of the major income of Google. As google makes money by running ads inside videos. It is that up to 30% of internet users use Adblock and due to which google faces cut down in there income.
Via : Adblock Forum