Can't tag snapshot in AWS::EC2 with ruby SDK

Question

I'm using the AWS SDK and I not able to tag an existing snapshot. It says the snapshot does not exits even though you can see that my test object is an AWS::EC2::Snapshot. Whats up ?!?!

irb(main):017:0> test
=> <AWS::EC2::Snapshot id:snap-XXXXXXXX>
irb(main):018:0> test.tag('auto_delete')
AWS::EC2::Errors::InvalidSnapshot::NotFound: The snapshot 'snap-XXXXXXXX' does not exist.
    from /Library/Ruby/Gems/2.0.0/gems/aws-sdk-1.25.0/lib/aws/core/client.rb:366:in `return_or_raise'
    from /Library/Ruby/Gems/2.0.0/gems/aws-sdk-1.25.0/lib/aws/core/client.rb:467:in `client_request'
    from (eval):3:in `create_tags'
    from /Library/Ruby/Gems/2.0.0/gems/aws-sdk-1.25.0/lib/aws/ec2/tagged_item.rb:31:in `add_tag'
    from (irb):18
    from /usr/bin/irb:12:in `<main>'
irb(main):019:0>