AWS & Packer: x509: certificate signed by unknown authority

I am trying to create AMI from an AWS instance with packer.

I get this error:

Build ‘amazon-ebs.example’ errored after 37 seconds 148 milliseconds: error validating regions: RequestError: send request failed
caused by: Post “https://ec2.us-east-1.amazonaws.com/”: x509: certificate signed by unknown authority

Has anybody else seen this?

Thanks
Ken