This is a small post to explain how to make the Google XML SiteMap plugin work fine if you have installed W3 Total Cache too. I chose not to talk about this in my previous post, about the migration from DotClear 2 to WordPress 3, because I think this would be more easy to find out as a post of its own.
The problem is that, by default, you won't be able to update your site map anymore, once you have installed W3 Total Cache. You're likely to get this error:
The trick to solve this error is to change the detection mode from automatic, to custom location, and to fill the form with the correct location of your sitemap on the hard drive of your server:
You can now rebuild your sitemap, and all should be working fine by now.