JavaScript - Checkbox onchange function is not executing the whole way through

I have an input of type checkbox with an onchange event as shown below:

<input type="checkbox" runat="server" id="cbWarehouse" onchange="disableAllButtons()"/>

<script>
    function disableAllButtons()
    {
        // gvDetail
        var gvDetail = document.getElementById("<%=gvDetail.ClientID %>");
        var gvDetailControls = gvDetail.getElementsByTagName("input");
        for (i = 0; i < gvDetailControls.length; i++)
        {
            gvDetailControls[i].disabled = true;
        }

        // gvSummary
        var gvSummary = document.getElementById("<%=gvSummary.ClientID %>");
        var gvSummaryControls = gvSummary.getElementsByTagName("input");
        for (i = 0; i < gvSummaryControls.length; i++)
        {
            gvSummaryControls[i].disabled = true;
        }
    }
</script>

This function's purpose is to disable all buttons in two GridViews - gvSummary and gvDetail. However, it only disables the buttons in whichever GridView I mention first in the JS function. I.e. in the example above, the buttons in gvDetail will be disabled but not in gvSummary.

So it seems that the function stops halfway through..?

Anyone have any ideas where I am going wrong?