I installed the sitemap, ran the Sitemap generator without any problems.
at the end it says:
[create sitemap file] filename: sitemap_3.xml.gz, number of urls: 19576 [2,130.2Kb mem used] [6s (+0s)]
[create sitemap index] filename: sitemap_index.xml.gz, number of sitemaps: 3 [2,130.8Kb mem used] [6s (+0s)]
Sitemap has been created. Click here to return [2,130.3Kb mem used] [8s (+2s)]
But when I download the sitemap_index.xml.gz, it is only 164 bytes and has this for content:
Sorry, but the file you requested is not available.
<p>Please <a href="/">start here</a>.