Why is this an issue?

Nested Select Case structures are difficult to understand because you can easily confuse the cases of an inner Select Case as belonging to an outer statement. Therefore nested Select Case statements should be avoided.

Specifically, you should structure your code to avoid the need for nested Select Case statements, but if you cannot, then consider moving the inner Select Case to another function.

Noncompliant code example

Public Sub Foo(A As Integer, B As Integer)
    Select Case A
        Case 0
            ' ...
        Case 1
            Select Case B   ' Noncompliant; nested Select Case
                Case 2
                    ' ...
                Case 3
                    ' ...
                Case 4
                    ' ...
                Case Else
                    ' ...
            End Select
        Case 2
            ' ...
        Case Else
            ' ...
    End Select
End Sub

Compliant solution

Public Sub Foo(A As Integer, B As Integer)
    Select Case A
        Case 0
            ' ...
        Case 1
            HandleB(B)
        Case 2
            ' ...
        Case Else
            ' ...
    End Select
End Sub