Not visible textbox on selecteditemchanged in dropdownlist.

<asp:DropDownList ID="ddlsellprty" runat="server" AutoPostBack="true"
                                onselectedindexchanged="ddlsellprty_SelectedIndexChanged"></asp:DropDownList>

protected void ddlsellprty_SelectedIndexChanged(object sender, EventArgs e)
    {
        string check = ddlsellprty.SelectedItem.Value;
        if (check == "Other")
        {
            txtother.Visible = true;
        }


    }