VS2012 / Javascript

This doesn't work and I don't know why?
    <script type="text/javascript">
        function GameDate() {
                document.getElementById('txt_GameDate.ClientID').disabled = 'false';
                document.getElementById('txt_GameDate.ClientID').disabled = 'true';

I want to enable a textbox when the checkbox is checked off!

I get this error when I click the Check Box:
0x800a138f - JavaScript runtime error: Unable to get property 'checked' of undefined or null reference
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Duy PhamFreelance IT ConsultantCommented:
I think it is because no control exists with such chk_AllGameDate.ClientID ID. Try to remove .ClientID (also in txt_GameDate.ClientID).

Are you developing an asp.net web app? If yes then you'd better use server tag <%= chk_AllGameDate.ClientID %> instead.

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smithmrkAuthor Commented:
This Fixed my issue:

use server tag <%= chk_AllGameDate.ClientID %>
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