TypeOf someobject IsNot TypeOfObject

Make sure you only use on ref Types. For Example:

'this will work Dim yourVar As New Object 'returns False If TypeOf yourVar IsNot Object Then 'code here End If 'this won't work Dim yourVar As Integer 'error If TypeOf yourVar IsNot Integer Then 'code here End If

It has nothing to do with ref / value types:

Dim i as Object If TypeOf i IsNot Object Then DoSomething() End If

This does not compile. It gives two errors:
-"BC30224: 'Is' expected." squiggling "IsNot"
-"BC30109: 'System.Object' is a class type and cannot be used as an expression." squiggling "Object".
If I rewrite to:

Dim i as Object If Not TypeOf i Is Object Then DoSomething() End If

This compiles perfectly.

The thing is that "typeof ... is" is a single operator - the "is" in there is not related to the "is" operator. As such, when the IsNot operator was introduced, it did not affect other syntaxes that use the text "is", such as the typeof...is operator or the "case is" statement.

Changes have been considered to make the syntax a bit more coherent along other is usages, but it was decided not to make them in VB 2005. They might be considered for the next version.