adding validator controls dynamically to a page

[sonic]

I am trying to dynamically load a validator and must be missing
something elementary here.

I extended TextBox control to add some functionality to it. One new
feature it contains is IsRequired property. if true, the control will
render it self differently, and should add a RequiredFiledVa lidator
control to the page.

so in my controls render event, i am adding the following:

if ( this.IsRequired ) {
...// handle visual stuff ( works fine )
RequiredFieldVa lidator v = new RequiredFieldVa lidator();
v.ControlToVali date = this.ID;
v.EnableClientS cript = true;
v.ErrorMessage = "*";

this.Page.Contr ols.Add(v);
}

the following code will compile, and i will get a runtime error that
the validator control could not find the ControlToValida te target.
"Unable to find control id 'TransactionTyp eList' referenced by the
'ControlToValid ate' property of ''.
i thought, this is understandably so, since MyTextBox could be rendered
in another user control ( vs Page ).

so i tried modifying the last line to
this.NamingCont ainer.Controls. Add(v);
but i get another runtime error after that of
The Controls collection cannot be modified because the control contains
code blocks (i.e. <% ... %>).

am i going about this all wrong?