[Plugin: Google XML Sitemaps] Fopen error for sitemap.xml

I have some company complaining of problems trying to read my sitemap from my WordPress blog with the Google XML Sitemap plugin.

<b>Warning</b>: fopen(/home3/dragonb2/public_html/wp-app.php/sitemap.xml) [function.fopen]: failed to open stream: Not a directory in <b>/home3/dragonb2/public_html/wp-content/plugins/google-sitemap-generator/sitemap-core.php</b> on line <b>1623</b>

<b>Warning</b>: gzopen(/home3/dragonb2/public_html/wp-app.php/sitemap.xml.gz) [function.gzopen]: failed to open stream: Not a directory in <b>/home3/dragonb2/public_html/wp-content/plugins/google-sitemap-generator/sitemap-core.php</b> on line <b>1636</b>

Is there any solution for this that developer knows of?

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