Help: ZwFsControlFile() not working in 2K kernel mode

Hi All,
I want to get the VCN->LCN mapping for a file in 2K kernel mode using
ZwFsControlFile() . The same function is working fine in XP & 2K3 (kernel
mode).
So what is the required that is to be done.
Thanks in advance,

-Vipul Jain.
PS: The VCN->LCN mapping function for a file is available & working in 2K
user mode using DeviceIoControl.