Emergency: After updating, site gone with Fatal Error message

After updating, nothing worked. All I get is this message:

Fatal error: Cannot redeclare class URI_Template_Parser in /home/jeymi/public_html/wp-content/plugins/wpmu-dev-plusone/lib/external/google/external/URITemplateParser.php on line 30

No site, no wordpress multisite, no nothing. Help, please, this is an emergency.