I'm using Yoast with WP e-Commerce.
All the sitemaps seem to generate OK, except the last three product sitemaps. Numbers 9, 10, and 11 fail. They either timeout (even after I set the execution limit to 60) or the page isn't found.
Since it's only a few of the sitemaps, I'm figuring it can't be the htaccess re-write problem or the execution timeout problem.
My sandbox/test site sitemap is at: