GetWindowThreadProcessId is returning 0 on windows server 2012R2

Hi Team,

On windows server 2012R2, using GetWindowThreadProcessId, I am unable to get process id of object of an excel application(Excel.Application) though the Hwnd of this object is getting send correctly. 

On Dev machine(windows 7), this process id is getting returned correctly, looks like some issue with the server.

I need to find above process id so that I could so that I could kill it(after finding all excel processes on the server).

Can you please help me resolve this.

Thanks,

Salil