The Framework Gen.Ref. says "the input control fails validation if the value it contains does not change from its initial value. By default the initial value is an empty string." It continues with "the InitialValue property does not set the default value of the control. It simply indicates the value that you do not want the user to enter in the input control." But the framework seems to contradict itself by saying that the InitialValue property "gets or sets the initial value of the associated input control." So if I did not set my InitialValue property then I assume its an empty string, and if there was no entry in the associated text box then I also assume its an empty string. But why doesn't the error message appear when the rule seems to be broken that there is no change from empty string to something other than an empty string?

Just a quick thought but is your ControlToValidate property set to the correct textbox? Otherwise the default InitialValue if left blank will assume that a blank text box is a rule violation and should throw the error.