title: value of property security group must be of type list of string
body: <pre><code>Parameters:
    KeyName:
      Description: Name of an existing EC2 KeyPair to enable SSH access to the instance
      Type: 'AWS::EC2::KeyPair::KeyName'
      ConstraintDescription: must be the name of an existing EC2 KeyPair.
  
    MySubnet:
      Description: My subnet from my VPC
      Type: 'AWS::EC2::Subnet::Id'
      Default: subnet-YYYYYYYY
    
    MySG:
      Description: My Security Group from my VPC
      Type: 'AWS::EC2::SecurityGroup::GroupName'
      Default: SG-YYYYYYYY
     
  Resources:
  
    Ec2Instance:
      Type: AWS::EC2::Instance
      Properties:
        InstanceType: t2.micro
        ImageId: ami-09e67e426f25ce0d7
  
        SecurityGroups: !Ref MySG
  
        SubnetId: !Ref MySubnet
        
        KeyName: !Ref KeyName
    
        
  </code></pre>
  <p>I have this above cloudformation template code which returns &quot;Value of property SecurityGroups must be of type List of String&quot;, my vpc and security groups are simplified in a different cloudformation template, and i want to launch an ec2 in a specific Security group.</p>