AWS SDK for .NET Documentation
Cause Property
AmazonAmazon.SimpleWorkflow.ModelRequestCancelExternalWorkflowExecutionFailedEventAttributesCause Did this page help you?   Yes   No    Tell us about it...
The cause of the failure to process the decision. This information is generated by the system and can be useful for diagnostic purposes.
Note:
If cause is set to OPERATION_NOT_PERMITTED, the decision failed because it lacked sufficient permissions. For details and example IAM policies, see Using IAM to Manage Access to Amazon SWF Workflows.

Constraints:

Allowed Values
UNKNOWN_EXTERNAL_WORKFLOW_EXECUTION, REQUEST_CANCEL_EXTERNAL_WORKFLOW_EXECUTION_RATE_EXCEEDED, OPERATION_NOT_PERMITTED

Declaration Syntax
C#
public string Cause { get; set; }

Assembly: AWSSDK (Module: AWSSDK) Version: 1.5.60.0 (1.5.60.0)