In VB6 you may catch err as:
Private Sub DivideByZero()
On Error GoTo Err_Handler
    Dim num As Integer
    Dim zero As Integer
   
    num = 100 / zero
   
Exit_Eop:
    Exit Sub
Err_Handler:
    MsgBox ("Error Code : " & Err.number & vbCrLf & "Error Message : " & Err.Description)
End Sub

In C# the equivalent would be:
using System.Reflection;
private void DivideByZero()
{
 try
 {
  int zero = 0;
  int num = 100 / zero;
 }
 catch (Exception ex)
 {
  Type type = typeof(Exception);
  int errNo =  (int)type.InvokeMember("HResult", System.Reflection.BindingFlags.DeclaredOnly   | BindingFlags.NonPublic | BindingFlags.Instance |  BindingFlags.GetProperty, null, ex, null);
  string errMsg =String.Format ("Error Code : {0}\r\nError Message : {1}",errNo, ex.Message);
  MessageBox.Show(errMsg);
 }
}
Please note that the error code in C# would not match with what you get in VB6.


Thanks to : Willy Denoyette
at: http://www.techtalkz.com/c-c-sharp/121497-get-error-number-2.html