title: Template format error: unsupported structure seen in AWS CloudFormation
body: <p>I am trying to validate an AWS example CloudFormation template using a command like:</p>
  
  <pre><code>▶ aws cloudformation validate-template --template-body template.yml
  </code></pre>
  
  <p>This leads to the following error message:</p>
  
  <pre><code>An error occurred (ValidationError) when calling the ValidateTemplate operation:
    Template format error: unsupported structure. 
  </code></pre>
  
  <p>I tried this on many templates, including example templates from the AWS documentation. So I know the templates are okay.</p>
  
  <p>What am I doing wrong?</p>