[Plugin: Google XML Sitemaps] Error loading stylesheet: An XSLT stylesheet does not have an XML mime

I have had this problem since upgrading to 2.8 and 2.8.1.

What has worked for me is disabling all my plugins except Google XML Sitemaps, then rebuilding the sitemap. That definitely works, but it is a nuisance. I guess it is a memory problem.

When you rebuild the sitemap, the status box will tell you how much memory was used. You can try increasing the memory in the advanced section of the Google XML Sitemaps plugin settings. I still have the problem sometimes, even though I have done this.