[Plugin: WordPress SEO by Yoast] WordPress SEO sitemap redirect error

I updated WordPress SEO yesterday to 0.2.3.3 and my sitemap has since been generating errors on Google Webmaster. The error for the xml file states ‘Your Sitemap appears to be an HTML page. Please use a supported sitemap format instead’. And the gz. file states a 302 redirect error.

I have made no changes to the site except update WordPress SEO. The plugin was working really well before the update and I was very pleased with it. I rebuilt the sitemap after doing the update, which seemed to fix the errors temporarily but it is showing them again this morning.

I am using wordpress 3.0.4. And the site is https://www.carpentershrewsbury.org.uk. Any advice for a non-technical user would be very much appreciated. Thank you.