Registry.LocalMachine.OpenSubK...

I am programming with Visual Basic in Visual Studio 2010. The following code returns null for rk

        Dim SoftwareKey As String
        Dim rk As RegistryKey
        SoftwareKey = "SOFTWARE\Microsoft\Windows\CurrentVersion\Installer\UserData\S-1-5-18\Products"
        rk = Registry.LocalMachine.OpenSubKey(SoftwareKey)
 

However, I know that the sub key exists because I can see it when I run regedit.exe, the registry editor. What am I doing wrong?