Error Some of field value is invalid
This problem comes from other plugins. Some plugin adds some hidden field in Comment Form using form hooks. This plugin expect submitted data but wpDiscuz doesn't support it and it doesn't send that data so you get such error. Please deactivate all plugins (Antispam, Security, Captcha, Comment plugins, etc..) and test it again. This problem is not wpDiscuz core problem so it can't be fixed from wpDiscuz side.