Invalid Postback or Call Back Argument error

Hi,

Recently, I added a button, a textbox and a jquery code. On click of button the textbox value was been captured in the dropdown. All my code is working fine. But, when I fill the other data and submit the form, It gives me the below error.

Couldn't know where I am making mistake.

Also see the vode for your reference:-

J

 <script type="text/javascript">
        $('#ctl00_ContentPlaceHolder1_txtOtherBusiness').hide();
        $('#ctl00_ContentPlaceHolder1_btnbusinessAdd').click(function (event) {
            event.preventDefault();
            if ($('#ctl00_ContentPlaceHolder1_txtOtherBusiness').is(':visible')) {
                var text = $('#ctl00_ContentPlaceHolder1_txtOtherBusiness').val();
                var dropDown = $('#ctl00_ContentPlaceHolder1_ddlBusinessUnit');
             
                var text = $('#ctl00_ContentPlaceHolder1_txtOtherBusiness').val();
                var itemVal = 1; // some value for option                
                var newItem = $('<option/>').val(itemVal).text(text).appendTo(dropDown);
                $('#ctl00_ContentPlaceHolder1_txtOtherBusiness').hide();
            }
            else {
                $('#ctl00_ContentPlaceHolder1_txtOtherBusiness').show();
            }
        });
    </script>

Button and Textbox code:-

<asp:DropDownList CssClass="txtfld-popup" ID="ddlBusinessUnit" runat="server"></asp:DropDownList>
                        <asp:Button ID="btnbusinessAdd" runat="server" Width="63" Text="Add" CausesValidation="false"/>
                        <asp:TextBox ID="txtOtherBusiness" runat="server"  CssClass="txtfld-popup"></asp:TextBox>
                        <asp:RequiredFieldValidator CssClass="error_msg" ID="reqBusinessUnit" ControlToValidate="ddlBusinessUnit" runat="server" ErrorMessage="Please enter business unit" InitialValue="--Select--" SetFocusOnError="true"></asp:RequiredFieldValidator>

Please help.