500 Internal server error?

I installed WP some 4 months ago and have made no changes, now whenever I go to publish a new psot, I get 500 Internal error message, I have been into my cpanel and copied all the code it says which is below.

Can anyone provide me with a solution please?

[Tue Aug 18 10:45:26 2009] [error] [client 82.159.178.6] File does not exist: /home/wwwlcde/public_html/500.shtml, referer: https://www.lcdenclosure.co.uk/news/wp-admin/post.php?action=edit&post=228
[Tue Aug 18 10:44:49 2009] [error] [client 82.159.178.6] File does not exist: /home/wwwlcde/public_html/500.shtml, referer: https://www.lcdenclosure.co.uk/news/wp-admin/post.php?action=edit&post=228
[Tue Aug 18 10:43:49 2009] [error] [client 82.159.178.6] File does not exist: /home/wwwlcde/public_html/500.shtml, referer: https://www.lcdenclosure.co.uk/news/wp-admin/post.php?action=edit&post=228
[Tue Aug 18 10:42:49 2009] [error] [client 82.159.178.6] File does not exist: /home/wwwlcde/public_html/500.shtml, referer: https://www.lcdenclosure.co.uk/news/wp-admin/post.php?action=edit&post=228
[Tue Aug 18 10:41:48 2009] [error] [client 82.159.178.6] File does not exist: /home/wwwlcde/public_html/500.shtml, referer: https://www.lcdenclosure.co.uk/news/wp-admin/post.php?action=edit&post=228
[Tue Aug 18 10:40:26 2009] [error] [client 82.159.178.6] File does not exist: /home/wwwlcde/public_html/404.shtml
[Tue Aug 18 10:40:26 2009] [error] [client 82.159.178.6] File does not exist: /home/wwwlcde/public_html/favicon.ico
[Tue Aug 18 10:39:15 2009] [error] [client 149.32.192.34] File does not exist: /home/wwwlcde/public_html/404.shtml
[Tue Aug 18 10:39:15 2009] [error] [client 149.32.192.34] File does not exist: /home/wwwlcde/public_html/none
[Tue Aug 18 10:39:12 2009] [error] [client 149.32.192.34] File does not exist: /home/wwwlcde/public_html/404.shtml
[Tue Aug 18 10:39:12 2009] [error] [client 149.32.192.34] File does not exist: /home/wwwlcde/public_html/favicon.ico
[Tue Aug 18 10:37:53 2009] [error] [client 72.52.255.82] PHP Fatal error: Class ‘xml_sitemap’ not found in /home/wwwlcde/public_html/news/wp-content/plugins/xml-sitemaps/xml-sitemaps.php on line 110
[Tue Aug 18 09:42:33 2009] [error] [client 71.28.48.108] File does not exist: /home/wwwlcde/public_html/404.shtml
[Tue Aug 18 09:42:33 2009] [error] [client 71.28.48.108] File does not exist: /home/wwwlcde/public_html/favicon.ico
[Tue Aug 18 09:37:42 2009] [error] [client 72.52.255.82] PHP Fatal error: Class ‘xml_sitemap’ not found in /home/wwwlcde/public_html/news/wp-content/plugins/xml-sitemaps/xml-sitemaps.php on line 110
[Tue Aug 18 09:23:09 2009] [error] [client 195.62.192.51] File does not exist: /home/wwwlcde/public_html/404.shtml
[Tue Aug 18 09:23:09 2009] [error] [client 195.62.192.51] File does not exist: /home/wwwlcde/public_html/favicon.ico
[Tue Aug 18 08:49:13 2009] [error] [client 63.77.11.180] File does not exist: /home/wwwlcde/public_html/404.shtml
[Tue Aug 18 08:49:13 2009] [error] [client 63.77.11.180] File does not exist: /home/wwwlcde/public_html/favicon.ico
[Tue Aug 18 08:49:10 2009] [error] [client 63.77.11.180] File does not exist: /home/wwwlcde/public_html/404.shtml
[Tue Aug 18 08:49:10 2009] [error] [client 63.77.11.180] File does not exist: /home/wwwlcde/public_html/favicon.ico