title: AWS ECR CF template fails with 'Invalid repository policy provided'
body: <p>This CF template fails:</p>
  
  <pre><code>  MyECSrepo:
      Type: "AWS::ECR::Repository"
      Properties:
        RepositoryName: !Ref RepoName
        RepositoryPolicyText:
          Version: "2012-10-17"
          Statement:
            - Sid: AllowAll
              Effect: Allow
              Principal: 
                AWS:
                  - arn:aws:iam::00000000000:group/admin
              Action:
            - "ecr:*"
  </code></pre>
  
  <p>The stack creation produces this error:</p>
  
  <p>Invalid parameter at 'PolicyText' failed to satisfy constraint: 'Invalid repository policy provided'</p>
  
  <p>What might the problem be?</p>