Try
Dim aa As Object
aa = Registry.GetValue("HKEY_CURRENT_USER\Software\Avira\AntiVir Desktop", "LastCommandLine", Nothing)
Can you see why? The key value you really need is "HKEY_CURRENT_USER\Software\Avira\AntiVir Desktop"; and the double '\\' simply means escaped '\', by C# syntax, not VB.NET. To make C# code similar, use verbose modifier '@':
object aa = Registry.GetValue(@"HKEY_CURRENT_USER\Software\Avira\AntiVir Desktop","LastCommandLine", null);
Better now? :-)
—SA