[Plugin: Google XML Sitemaps] Permission Error using Google XML Sitemap Generator plugin

I’m getting the following errors when trying to tun the xml sitemap generator. I’ve checked the permissions for the files and the root folder and they are set to 777. The site is on a Windows 2003 server.

Warning: fopen(/sitemap.xml) [function.fopen]: failed to open stream: Permission denied in E:\hshome\xxxxxxxx\xxxxxxxxxx.xxx\web\wp-content\plugins\google-sitemap-generator\sitemap-core.php on line 1623

Warning: gzopen(/sitemap.xml.gz) [function.gzopen]: failed to open stream: Permission denied in E:\hshome\xxxxxxxx\xxxxxxxxxx.xxx\web\wp-content\plugins\google-sitemap-generator\sitemap-core.php on line 1636

Any comments and/or suggestions would be gratefully received (preferably before I tear my hair out).