Same problem here. After upgrade to 1.6.1.7 I've got error
Fatal error: Cannot redeclare class Swift in /home/www/ajaxjihlava.cz/subdomeny/www/tools/swift/Swift.php on line 32
It happens on "request new password" form and also on order confirmation (I think it happens everytime an email is send on confirmation)
I was trying to override tools/swift/ files with older version, but it cause several more errors with mailjet module so it's not solution