regwrite not working in windows 7

Hello,

I am trying to delete and add some registry keys in windows 7. Please can someone help me with this.
Can someone show me what I am doing wrong to get this to work.
; Write a single REG_SZ value
RegWrite("HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\","DefaultUserName","REG_SZ","Pilot")