Bear in mind I don't work with the team responsible for the SDK, you should follow up with a bug report on your end. I'll likely reach out internally as well.

I had assumed you were using local WSDL files, it sounds like that will correct the issue until the WSDL is fixed on the installation base for ESX 4.1. Bear in mind for most users, they do not use ESX WSDL files, they typically use a wsdl compiler to interact with the SDK. No offense intended to your code base