Hi Ivan,
It is working for me at its normal location
http://www.bulgarianplates.com/sitemap_index.xml.
One of the usual issues is that sometimes permalinks need to be re-saved for it to show up
Hi I am away from a real computer at the moment so cannot download to check but it sounds like the plugin is not translated. Search for the .po files that have bg_BG. The other possibility if the plugin is translated is that you havent added the language code to wp-config.php
I just checked my server and it is now not creating the sitemap at all which explains the 404.
No caching is switched on and the previous version also does not work.
