Just upgraded to v1.3 and the result as the complete failure of my site.
Error messages below:
Warning: require_once(functions/sitemap-functions.php) [function.require-once]: failed to open stream: No such file or directory in /home/referon/public_html/dev/wp-content/plugins/atlas-html-sitemap-generator/atlas-html-sitemap-generator.php on line 56
Fatal error: require_once() [function.require]: Failed opening required 'functions/sitemap-functions.php' (include_path='.:/usr/lib/php:/usr/local/lib/php') in /home/referon/public_html/dev/wp-content/plugins/atlas-html-sitemap-generator/atlas-html-sitemap generator.php on line 56
This affected the public site but also access to the admin site so without interacting directly with the db it wasn't even possible to deactivate the plugin.
I have now uploaded an older version of the plugin to my site bringing it back online.