Trouble to starting witw my first sitemap

Hi to all,
I have just installed xml sitemap, and I have this warning:
# warning: fopen() [function.fopen]: SAFE MODE Restriction in effect. The script whose uid is 1326 is not allowed to access /tmp/fileLot9OI owned by uid 1000 in /workdisk/home/web/www.rassavalsesia.com/htdocs/drupal/includes/file.inc on line 527.

# warning: fopen(/tmp/fileLot9OI) [function.fopen]: failed to open stream: Success in /workdisk/home/web/www.rassavalsesia.com/htdocs/drupal/includes/file.inc on line 527.

# The file could not be created.

# Unable to load site map. Make sure that there is an xmlsitemap directory in your files directory and that it is writable by Drupal.

the xmlsitemap in my files directory is writable, I hope somebody help me... thank's a lot!!
Magut