Sitemap can be read but has errors. An Invalid date was found. Sitemap Error

I got this following error in google webmaster tools "Sitemap can be read but has errors. An invalid date was found. please fix the date or formatting before resubmitting".
This is due to publication_date tag value is missing in sitemap.xml. After I updating the field in SQL and generated the sitemap, the error was disappeared.

Video GUIDE fixing Sitemap Error: