Error in Google Webmaster tools on subpage

I am using the 4b10 plugin. It works good no doubt. I have only one problem – in Google Webmaster Tools there is only one particular page which is showing error:

https://www.cphpvb.net/sitemap-page-2009-07.xml

Missing XML tag
Parent tag: urlset
Tag: url
This required tag is missing. Please add it and resubmit.

I am unsure why this empty page sitemap was generated at all.

https://www.ads-software.com/extend/plugins/google-sitemap-generator/