IUIAutomationElement FindAll/FindAllBuildCache gives null on some machines

Question

I am using UI Automation to get elements from a window.

Using the following API's
IUIAutomationElement::FindAll
IUIAutomationElement::FindAllBuildCache

This works on most of the machines and returns null on some machines, though the UIAutomation element is picked up correctly. Any idea why it does not work on some machines though they have same OS and Software, only the hardware is different.