Bernard,
ArrayList.IndexOf (CollectionBase.List.IndexOf) uses Object.Equals to
compare two objects, so to get ColVariables.IndexOf to work you need to
override Object.Equals in your Variable class:

Something like:

   Public Class Variable

       Private ReadOnly m_name As String
       Private ReadOnly m_value As Object

       Public Sub New(ByVal name As String, ByVal value As Object)
           m_name = name
           m_value = value
       End Sub

       Public Overloads Function Equals(ByVal value As Variable) As Boolean
           Return m_name = value.m_name AndAlso
m_value.Equals(value.m_value)
       End Function

       Public Overloads Overrides Function Equals(ByVal obj As Object) As
Boolean
           If TypeOf obj Is Variable Then
               Return Equals(DirectCast(obj, Variable))
           Else
               Return False
           End If
       End Function

   End Class

You may want to have VariableCollection (your ColVariables) inherit from
DictionaryBase or NameObjectCollectionBase instead of CollectionBase, as it
appears you have a collection of named objects.

Hope this helps
Jay