On occasion upgrading a WordPress plugin can cause trouble, notably the white screen of death. When this happens the fastest way to solve the problem is to disable all the plugins.
To do this, load up the WordPress database and locate the options table. Find the active_plugins record, record the contents, and then clear out the record.
Your WordPress site should display once again, minus your plugins. Now you can re-enable your plugins and diagnose why the misbehaving plugin screwed with ya. A quick link to this issue is at http://perishablepress.com/press/2008/02/18/quickly-disable-or-enable-all-wordpress-plugins-via-the-database/.