[Solved] JavaScript returns NaN value in ASP.Net

I don't know why I get this label value "NaN" each time I clear the TextBox where I use to multiply with another to display result in another label.

The result label is where the "NaN' shows when I clear textbox1

<div class="row">
    <div class="col-sm-5">
        <div class="form-group">
            <label runat="server" id="Label1" style="font-weight: 700;">No. of Authentications</label>
            <div class="input-group">
                <asp:TextBox ID="MultiText" runat="server" CssClass="form-control" Text="" Font-Size="14pt" placeholder="0" onKeyup="calculate();" />
            </div>
        </div>
    </div>
    <div class="col-sm-2">
        <div class="form-group">
            <label runat="server" id="Label9" style="font-weight: 700;"></label>
            <div class="input-group">
                <asp:Label ID="txtval" runat="server" Text="20" Style="display: none"></asp:Label>
            </div>
        </div>
    </div>
    <div class="col-sm-5">
        <div class="form-group">
            <label runat="server" id="Label2" style="font-weight: 700;">No. of Credits</label>
            <div class="input-group">
                <asp:Label ID="LblResult" runat="server" Text="0" Font-Size="14pt"></asp:Label>
            </div>
        </div>
    </div>
</div>

<script type="text/javascript">
    function calculate(e) {
        var txt1 = document.getElementById('MultiText').value;
        var txt2 = document.getElementById('txtval').innerHTML;
        document.getElementById('LblResult').innerHTML = parseFloat(txt1) * parseFloat(txt2);
    }
</script>