Error in XML & sitemap.xml

Hello,

I updated to the latest version of WP and the SEO plugin i.e. “google-sitemap-generator” and now I get the error:
Error loading stylesheet: A network error occurred loading an XSLT stylesheet:
http://<mysitename>/wp-content/plugins/google-sitemap-generator/sitemap.xsl

The error appears in Firefox, can’t see anything when using Chrome!

Thank you very much for any little help !