Wordpress stopped working after upgrade to version 3.2

As usual, as soon as I noticed the new version announcement at the top of the wordpress administration interface I instructed it to start. However, immediately after the upgrade to version 3.2 the wordpress installation stopped working.
I could not access wp-admin to try and fix whatever went wrong and, at the same time, the visitors would not be able to reach the blog.

So I went to check the server logs in cPanel and found out that the problem was somehow related to the WP to Twitter plugin, but how could I fix it without access to the administration panel?

The errors found:
[warn] mod_fcgid: stderr: PHP Warning: require_once() [function.require-once]: Unable to access /var/www/vhosts//httpdocs/wp-includes/class-json.php in /var/www/vhosts//httpdocs/wp-content/plugins/wp-to-twitter/functions.php on line 52
[warn] mod_fcgid: stderr: PHP Warning: require_once(/var/www/vhosts//httpdocs/wp-includes/class-json.php) [function.require-once]: failed to open stream: No such file or directory in /var/www/vhosts//httpdocs/wp-content/plugins/wp-to-twitter/functions.php on line 52
[warn] mod_fcgid: stderr: PHP Fatal error: require_once() [function.require]: Failed opening required '/var/www/vhosts//httpdocs/wp-includes/class-json.php' (include_path='.:/usr/share/pear') in /var/www/vhosts//httpdocs/wp-content/plugins/wp-to-twitter/functions.php on line 5

Easy solution: manually remove the plugin 

Accessing through FTP I went to the plugins directory inside wordpress instalation directory ( in my case it is /httpdocs/wp-content/plugins ) and removed the plugin directory 'wp-to-twitter'.
 Wordpress was available again so I went to wp-admin and 're'installed WP to Twitter. All configurations were kept so everything ended up alright.

Anyway, next time I'll make sure to check compatibility information regarding installed plugins and update them or disable before a wordpress upgrade.