Google Webmaster Error: Your Sitemap does not appear to be in a supported format

Plugin version 4.0.6

As of this version I am getting errors on every single sitemap subpage..

“Your Sitemap does not appear to be in a supported format. Please ensure it meets our Sitemap guidelines and resubmit.”

However when I go to http://www.validome.org/google/validate?url=http://www.kmcharityteam.co.uk/sitemap.xml&lang
=en&googleTyp=INDEX it says it’s valid. My sitemap is very simple, we only have about 150 pages, mostly posts. It doesn’t matter how many times I delete or resubmit, the error is the same.

Any ideas?

https://wordpress.org/plugins/google-sitemap-generator/