It seems that one of the plug-ins was causing guests to be unable to post comments. So we have disabled it. If you had trouble posting comments in the past, please accept our apology. In the meantime, some of the video tutorials are open to guests again.
With a large number of violators, we will disable video tutorials for guests at any time. Simply, don’t watch them unless you are willing to exchange information by posting comments.
Furthermore, guest video tutorials are all old. A few of them contain audio commentary. And they are in bad quality.