C1TaskDialog is only supported on Windows Vista or later. The control will simply not display on older versions of Windows and will not throw an exception. If the C1TaskDialog control is included in an application that may be run on previous versions of Windows – Windows XP, for example – you may want to specify an alternative dialog box so that important messages are displayed. You can do so by using the IsPlatformSupported property to detect the user's operating system.

For example:

To write code in Visual Basic

If C1TaskDialog.IsPlatformSupported Then
    c1TaskDialog1.Show()
Else
    ' Show a brief message with simple choice of the action
    Dim res As DialogResult = MessageBox.Show("Text", "Caption", MessageBoxButtons.YesNoCancel)
    If res = DialogResult.Yes Then
        ....
    End If
End If

To write code in C#

if (C1TaskDialog.IsPlatformSupported)
    c1TaskDialog1.Show();
else
{
    // Show a brief message with simple choice of the action
    DialogResult res = MessageBox.Show("Text", "Caption", MessageBoxButtons.YesNoCancel);
    if (res == DialogResult.Yes)
    {
        ...
    }
}