Carrington theme crashed after WP3.0 auto update

I updated my blog from within WP 2.9.1 to 3.0 and after that my site stopped working.

This is the message that I get:

Fatal error: Call to a member function add_rewrite_tag() on a non-object in /home/islando2/public_html/wp-includes/taxonomy.php on line 289

I am using the Carrington theme which have worked without any problems, until now.

This is what line 289 says in the taxonomy.php file says:

$wp_rewrite->add_rewrite_tag(“%$taxonomy%”, ‘([^/]+)’, $args[‘query_var’] ? “{$args[‘query_var’]}=” : “taxonomy=$taxonomy&term=”);

I can’t even access the admin interface as I get the same error message when trying to log on to my own blog.

What is the reason for this problem and how can I solve it? (I’m not a developer, just code aware on a general level.)

Should I downgrade my wp install and how is that done in an easy way?
Can I change my theme in another way as I cannot access my admin settings?

Help me out – I’m going nuts here and my site is down…..