What is likely to be the problem?
The Amazon Machine image used is not available in that region.
The AWS CloudFormation template needs to be updated to the latest version.
The VPC configuration parameters have changed and must be updated in the template.
The account has reached the default limit for VPCs allowed.
Explanations:
The availability of the Amazon Machine Image (AMI) is not likely to be the issue unless the template specifically references an unavailable AMI in that region.
The AWS CloudFormation template does not necessarily need to be updated to the latest version unless there is a specific issue with deprecated resources.
Changes in VPC configuration parameters are possible but not the most likely cause of stack failure, unless the template explicitly requires manual updates.
AWS accounts have default limits for the number of VPCs, and if this limit is exceeded, CloudFormation stacks will fail to deploy due to insufficient resources.
As I understand it, the answer is:
The account has reached the default limit for VPCs allowed.