Posts doesn't showing in wordpress 3.0.3

Thank you for your response.

I have followed the all steps in the link correctly
http://developersmind.com/2010/05/12/upgrading-wordpress-mu-2-9-2-to-wordpress-3-0-beta-with-multisite/

Also now I had added the following constant into the wp-config.php
define( “WP_USE_MULTIPLE_DB”, false );

Still now The site is having same issue.

Is the constant ‘NONCE_SALT’ must? If yes How Shall I get it?

Already this constant ‘NONCE_SALT’ still in the wp-config.php
then what is the cause of the issue ( Posts of the main blog doesn’t show )

Yes I have disabled all my plugins while upgrade then activate the all plugins after the upgrade.

My site is support multilingual. When I request the page like that http://www.example.com/it (italian) it will show page not found error also I couldn’t access anyone post or page.

I think the cause of the issue is in mod_redirect. Correct?