"This driver has been blocked from loading" in WindowsXP64O.S/Inte

I build my driver with WinDDK3790-WindowsXP64 or WindowsServer2003 IA64
compiler , no errors .
and install my driver/program in WindowsXP/Windows Server 2003 IA64 , use
Intel 64 CPU .
But it always gets the error code(1275-"This driver has been blocked from
loading") in DLL
after call StartService API , of course , every programming steps I had done
and I'm sure
no any errors with my DLL codes.
The most strange is if I build the same driver with WinDDK3790-WindowsXP64
or WinDDK3790-WindowsServer2003 AMD64 compiler ,
and install in different hardware environment(AMD64 CPU),O.S. is Windows
XP64/Windows Server 2003 AMD64.The program can works
fine.Why?? anyone knows??