Problems with customvalidator

I'm adding a textbox dynamically to a place holder inside an update panel depending on some choice the user make, I also add a required field validator and a custom validator. The textbox and the required field validator are working fine but the custom validator is not doing anything at all. Here is my code if anyone can figure out what I'm missing.
 
This is where I create and add the textbox and the validators to the placeholder:

//Create a textbox
tempTextBox = new TextBox();
tempTextBox.ID = parameterInfo.ParameterName + "TextBox";
_parameterPlaceHolder.Controls.Add(tempTextBox);

//Creates a require validation
tempRequiredValidator = new RequiredFieldValidator();
tempRequiredValidator.ID = parameterInfo.ParameterName + < ...