VB.Net has a root namespace and C# has a default namespace which is not the same. Because when you have a root namespace in VB.Net it will always add that before the namespace.
For example: if you have a rootnamepsace in VB.Net named namespace1 and then you add this to your file.
Namespace namespace1
Public Class class1
End Class
End Namespace
then you will have to refer to it as namespace1.namespace1.class1
in C# if you have a default namespace called namespace1 and you this in your file.
namespace namespace1{
public class class1{}
}
Then you can still just refer to it as namespace1.class1