Cloudformation fails with "AMI cannot be described"

The AMI was deleted by another user at the same time I did my edits.

The message "AMI cannot be described" actually means "AMI could not be found".

Hope this helps someone.

Thanks for sharing it actually means 'could not be found'.

In my case, it turned out one AWS account had no permission to pull the AMI hosted in another AWS account. Adding permissions solved the issue. Perhaps this info is helpful for others.