how to solve Microsoft JScript runtime error: Member not found.

<script type="text/javascript">
//<![CDATA[
var theForm = document.forms['form1'];
if (!theForm) {
    theForm = document.form1;
}
function __doPostBack(eventTarget, eventArgument) {
    if (!theForm.onsubmit || (theForm.onsubmit() != false)) {
        theForm.__EVENTTARGET.value = eventTarget;
        theForm.__EVENTARGUMENT.value = eventArgument;
        theForm.submit();
    }
}
//]]>
</script>

<asp:DropDownList ID="DropDownList1" runat="server" Height="16px" Width="106px"
                AutoPostBack="True" DataSourceID="AccessDataSource1" DataTextField="Role"
                DataValueField="Role">
            </asp:DropDownList>
            <asp:AccessDataSource ID="AccessDataSource1" runat="server"
                DataFile="~/App_Data/Database4.accdb"
                SelectCommand="SELECT [Role] FROM [Employee_Details]">
            </asp:AccessDataSource>