Upgraded to 3.0, instant Fatal error: Call to a member function add_rewrite_tag

All was working fine, and I updated from 2.9.2 to 3.0, and suddenly it went to a white screen that reads:
Fatal error: Call to a member function add_rewrite_tag() on a non-object in /home/lostinas/public_html/wp-includes/taxonomy.php on line 289

It was instant, and now I cannot access my site/dashboard on any browser or any computer. Every time I try to enter my site it gives me the above message.

Important to note that I can visit my site as a reader, but I cannot enter my site and do any work on it. PLEASE HELP!!