On the first look, your code seems to be OK. I'll change only this line:
If TypeOf ctr Is System.Windows.Forms.CheckBox Then
BTW: Never use names like: Control, etc as name of variable, because
Control[
^] defines the base class for controls, which are components with visual representation.
More about
TypeOf
operator:
http://msdn.microsoft.com/en-us/library/0ec5kw18.aspx[
^]