Hi,
I see that this plugin have a little bug. Create one more .xml of necessary and Google angry because he see it empty.

In my site, the last .xml file is the number 13 (sitemap13.xml). Listings finish at sitemap12.xml and the 13th have only this code :

Code:
Only registered members can view the code.

Google webmaster tools tell that the tag "url" is necessary, and give an error