I just upgraded to 3.4 and it broke my theme (Back My Book). I can see the main page, but when I try to login to WP Admin I get an error:
Fatal error: Cannot redeclare class Custom_Image_Header in /wp-admin/custom-header.php on line 16
I have the default themes like 2010 and 2011 installed and I've been keeping them updated. Is there a way to change the theme by editing a file somewhere so I can bypass this error to get back into my wordpress? Or is the entire site hosed and does it need to be reinstalled after the offending theme is deleted?