Writereg Problem

Hi,

When i try to write something in "HKLM" Nothing Happened
But when i try to write something in "HKCU" it Worked successfully

HKEY_LOCAL_MACHINE
WriteRegStr HKLM "SOFTWARE\Test" "Test" "Test"

HKEY_CURRENT_USER
WriteRegStr HKCU "SOFTWARE\Test" "Test" "Test"

Whats the Problem???
System:
Windows 7 (64-bit)

THANKS