[Plugin: Google XML Sitemaps] XML generator plugin can't write to files

My QNAP has a web directory like this.

share -> web -> wordpress -> wp-content -> plugins

After installing the plugin I added two files sitemap.xml and sitemap.xml.gz and placed them both in the web directory and the wordpress directory. I have tried both 755 and 777 chmod’s but still getting the error that it can’t write to these files and when you check the link below you can see that is is empty.

http://www.mackconsult.com/sitemap.xml

Not sure what to do ……..

http://wordpress.org/extend/plugins/google-sitemap-generator/