We've been having some problems with Google Webmasters Tools lately. Google's returning 404 on some of our articles. Can you anyone please explain why Google Webmasters Tools returns this error and how to fix it?
There are likely two problems on your site.
Put below two lines in your .htaccess file
php_value session.use_only_cookies 1 php_value session.use_trans_sid
And then put a rule in to strip session ids off of URLs with 301 redirects.