500 Internal Server Error – When editing posts.

Hi,

When I update a post/page and hit ‘update page’ 90% time I get an error:

http://www.mydomain.com/wp-admin/page.php?action=edit&post=41
&_wp_original_http_referer=http%3A%2F%2Fwww.mydomain.com%2Fwp-admin%2Fedit-pages.php&message=1

If I remove all past post=41 it then works eg:

http://www.mydomain.com/wp-admin/page.php?action=edit&post=41

I looked at my hosting error logs as and it looks like this:

/home/inspired/public_html/stanways/500.shtml, referer: http://www.thestanways.com/wp-admin/page.php?action=edit&post=41
/home/inspired/public_html/stanways/404.shtml
/home/inspired/public_html/stanways/406.shtml

Can anyone help and tell me why I am getting these error messages and when the flash uploader does not work.

Thanks