C1TaskbarButton is only supported by Windows 7. The control will not display on older versions of Windows, but it will not throw an exception if the user is using an earlier version of Windows. If the C1TaskDialog control is included in an application that may be run on previous versions of Windows – Windows XP or Vista, 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 C1TaskbarButton.IsPlatformSupported Then
   
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 (C1TaskbarButton.IsPlatformSupported)

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