I wanted to dynamically add my user control as a child to another control.
I've used the code with new constructor, as I did for standard ASP.NET server controls and custom controls.
Dim ctrlInstances As SearchAreasInstancesUsc = new SearchAreasInstancesUsc() 'Incorrect
tCell.Controls.Add(ctrlInstances)
Then I found that declaratively defined( in ASCX markup) controls are not initialized and set to null.
Of course, I should LoadControl to allow ASP.NET to initialize all declarations.
Dim ctrlInstances As SearchAreasInstancesUsc = LoadControl("SearchAreaInstancesUsc.ascx") 'correct
tCell.Controls.Add(ctrlInstances)
UPDATE: I strongly recommend to read a great atricle: TRULY Understanding Dynamic Controls -Parts 1-4.
(See also related Rendering ASP.NET Controls out of order and Rendering ASP.NET Controls out of place)
If you still need to use dynamic controls, some more examples are shown in Dynamically Created Controls: Dynamic Rows Sample (and Dynamically Created Controls in ASP.NET).