Two Tier CA Stack creation failure

[gwenvirtue]

When using this into an existing VPC following the steps here https://aws.amazon.com/blogs/security/how-to-enable-ldaps-for-your-aws-microsoft-ad-directory/ CloudFormation fails with the following errors:

ldaps-test-stack-3-TwoTierCAStack-R48WYZXB8D6L/351c4ba0-1776-11ed-998d-02b89f1999c9 was not successfully created: The following resource(s) failed to create: [SubCA].

If I look in the nested two-tier stack process, SubCA returns this: "Failed to receive 1 resource signal(s) within the specified duration" and begins the roll-back process.