Not sure if this is the problem, assuming you are using VB.Net (and not C# as the Tag says).
pnHolder.control.add(ctl)
It should read:
pnHolder.
controls.add(ctl)
You should also declare your user control before you can use it in your code. For example, I have a UserControl Class called _clUserControl. In the form where you wish to add the UserControl to the Panel control, you have to declare the UserControl first, e.g.:
Private clUserControl As New _clUserCOntrol
In your code where you wish to add the control to the Panel Control, simply add the the control:
myPanel.Controls.Add(clUserControl)