Required Validator still firing when textbox is not empty

Hi
I have a textbox on a form which is readonly, and has a required field validator set on. However, the textbox is populated by an action of a button. The action of the validator works when the textbox is empty,  but when the textbox is not empty it takes two clicks of the button to remove the error message. On the sub routine of the button I do set the required field validator to visibility to false, but this does not work.
Any solutions to prevent this from happening?

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