I am running into issue with only non-logged in guests who try to submit a comment. When you submit not logged, you get the red wpdiscuz-message-error error popup without a message and the comment does not submit. This does not happen with logged in users
This kind of issue is usually caused by either conflict with other plugins or the active theme.
Please deactivate all plugins (keep activated only the wpDiscuz), switch to some default theme and check again. If it works, activate the plugins/theme one by one and check after each activation to find a problem maker.
