I am using Yoast's WordPress SEO and here is what is happening:
1) The sitemap is generating and visible at domain.com/sitemap.xml
2) Sitemap is not visible through FTP at the root directory or anywhere else.
3) Followed the suggestions of making wp-content/uploads/wpseo permission set to 755.
4) Nothing is writing to that folder.
5) Google Webmaster Tools is encountering an error when trying to access the Sitemap.
Request assistance.