I feel like a total idiot. Thank you for catching it.

>You haven't instantiated an instance of MyDerivedClass (MyDerivedClass m_DerivedClass = new MyDerivedClass();)
>>Hi,
>>
>>I am having a problem that I will try to present here is a simplified manner:
>>
>>

>>public class MyBaseClass
>>{
>>    public DataSet myDataSet;
>>    
>>    public void MyMethod( string cStr )
>>    {
>>          // do something with the string cStr
>>   }
>>}
>>
>>public class MyDerivedClass : MyBaseClass
>>{
>>               // Nothing is this class, so far
>> }
>>
>>public partial class frmMyForm : Form
>>{
>>   private string cStr
>>   public MyDefirvedClass m_DerivedClass;
>>
>>   public frmMyForm()
>>   {
>>         InitializeComponent();
>>         m_DerivedClass.MyMethod( cStr );                        //  !!! This where I get error Null Reference
>>   }
>>
>>}
>>

>>
>>Note that the when I type m_DerivedClass in the frmMyForm constructor the intellisense shows the methods (MyMethod among them) of the class MyBaseClass so I know that I have declared "using" correctly. Why do I get the Null Reference on call MyMethod() then?
>>
>>TIA