CAL creation: Create default subnets step fails with invalid AWS availabilityZone

I tried to create an instance of "Intelligent Business Operations: SAP Process Orchestration 7.4 SPS 11 and SAP Operational Process Intelligence 1.0 SPS 09" a few moments ago.

However the "Create default subnets" step failed with the following message:

The error is:

com.amazonaws.AmazonServiceException: Value (us-east-1a) for parameter availabilityZone is invalid. Subnets can currently only be created in the following availability zones: us-east-1d, us-east-1c, us-east-1e, us-east-1b. (Service: AmazonEC2; Status Code: 400; Error Code: InvalidParameterValue

Any ideas how to correct this?

Br,

     Panu