Every time I try to grab an Automation Activity via the SOAP API, I'm told "AutomationTasks" does not exist as a property of object_type of "Automation". The documentation says otherwise (https://developer.salesforce.com/docs/atlas.en-us.mc-apis.meta/mc-apis/automation.htm).
Best Answer
Not all properties of objects are "Retrievable". The easiest way to check which properties can be retrieved is by issuing a Describe request against the API for the object. "AutomationTasks" is marked as not retrievable:
Request
Method = "POST" and SoapAction = "Describe"
Response