String was not recognized as a valid DateTime

[PetroTiburcio]

I am getting this error whenever I leave my drop down lists blank: "String was not recognized as a valid DateTime". My code is below:

aspx:

<asp:DropDownList ID="cboDay" runat="server" Width="55px" Height="32px" AppendDataBoundItems="true">
                <asp:ListItem></asp:ListItem></asp:DropDownList >
    <asp:DropDownList ID="cboMonth" runat="server" Width="80px" Height="30px" AppendDataBoundItems="true">
                <asp:ListItem></asp:ListItem></asp:DropDownList>
        <asp:DropDownList ID="cboYear" runat="server" Width="65px" Height="30px" AppendDataBoundItems="true">
                <asp:ListItem></asp:ListItem></asp:DropDownList>
code behind:
 
 protected void Page_Load(object sender, EventArgs e)
 {
        if (!IsPostBack)
        {
            GetDaysListed(cboDay);
            GetMonthsListed(cboMonth);
            GetYearsListed(cboYear);
        }
 }
 protected void btnSave_Click(object sender, EventArgs e)
    {
        try
        {
            if (txtfname.Text == String.Empty)
            {
                lblname.Text = "First Name Required";
                lblname.Visible = true;
            }
            if (txtlname.Text == String.Empty)
            {
                lbllname.Text = "Last name Required";
                lbllname.Visible = true;
            }
            else
            {
                SqlConnection con = new SqlConnection("Data Source=GATE-PC\\SQLEXPRESS;Initial Catalog=dbProfile;Integrated Security=True");
                SqlCommand cmd = new SqlCommand("qryINSERTprof", con);
                cmd.CommandType = System.Data.CommandType.Text;
 
                String str = cboDay.SelectedItem.Text + "/" + cboMonth.SelectedItem.Text + "/" + cboYear.SelectedItem.Text;
                lbltxtage.Text = str;
                DateTime dt = Convert.ToDateTime(str);
 
                string bdate = lbltxtage.Text;
                DateTime dts = DateTime.Parse(bdate);
                TimeSpan d = DateTime.Now.Subtract(dts);
                double years = d.TotalDays / 365;
                int months = (int)((years - (int)years) * 12);
                txtage.Text = ((int)years).ToString();
 
                Response.Write(dt.ToString("dd/MM/yyyy", System.Globalization.CultureInfo.InvariantCulture));
                cmd.Parameters.AddWithValue("@Lname", txtlname.Text);
                cmd.Parameters.AddWithValue("@Mname", txtmname.Text);
                cmd.Parameters.AddWithValue("@Fname", txtfname.Text);
                cmd.Parameters.AddWithValue("@BirthDate", lbltxtage.Text);
                cmd.Parameters.AddWithValue("@age", txtage.Text);
                cmd.CommandType = System.Data.CommandType.StoredProcedure;
                con.Open();
                cmd.ExecuteNonQuery();
                Response.Write("<script>alert('Record Successfully Added');</script>");
                clear();
            }
        }
        catch (Exception exe)
        {
            throw exe;
        }
 
    }
public void GetDaysListed(DropDownList DDDayList)
    {
        for (int i = 1; i < 32; i++)
        {
            ListItem list = new ListItem();
            list.Text = i.ToString();
            list.Value = i.ToString();
            DDDayList.Items.Add(list);
        }
        ListItem mlist = new ListItem();
        mlist.Text = null;
        mlist.Value = null;
        mlist.Selected = true;
        DDDayList.Items.Add(mlist);
    }
 
 
    public void GetMonthsListed(DropDownList DDMonthList)
    {
        DateTime month = Convert.ToDateTime("1/1/2007");
        for (int i = 0; i < 12; i++)
        {
 
 
            DateTime NextMont = month.AddMonths(i);
            ListItem list = new ListItem();
            list.Text = NextMont.ToString("MMMM");
            list.Value = NextMont.Month.ToString();
            DDMonthList.Items.Add(list);
        }
 
 
        ListItem mlist = new ListItem();
        mlist.Text = null;
        mlist.Value = null;
        mlist.Selected = true;
        DDMonthList.Items.Add(mlist);
    }
 
 
    public void GetYearsListed(DropDownList DDYearList)
    {
        int yearLast = DateTime.Now.Year + 18;
        int yearThen = yearLast - 90;
        for (int i = yearThen; i < yearLast; i++)
        {
            ListItem list = new ListItem();
            list.Text = yearThen.ToString();
            list.Value = yearThen.ToString();
            DDYearList.Items.Add(list);
            yearThen += 1;
        }
 
        ListItem mlist = new ListItem();
        mlist.Text = null;
        mlist.Value = null;
        mlist.Selected = true;
        DDYearList.Items.Add(mlist);
    }
    public string GetAge(DateTime dateOfBirth)
    {
        int iToday = int.Parse(DateTime.Today.ToString("yyyyMMdd"));
        int iDateOfBirth = int.Parse(dateOfBirth.ToString("yyyyMMdd"));
 
        string diff = (iToday - iDateOfBirth).ToString();
        string age = diff.Substring(0, diff.Length - 4);
 
        return age;
    }
my query:
 
ALTER PROCEDURE qryINSERTprof
    @Fname Varchar(50),
    @Mname Varchar(50),
    @Lname Varchar(50),
    @BirthDate datetime,
    @age varchar(50)
AS
    BEGIN
        INSERT INTO Profile ( Fname, Mname, Lname, BirthDate, Age )
VALUES (@Fname, @Mname, @Lname, @BirthDate, @age)
 
    END
    RETURN

Any help would be appreciated. Thanks in advance.

[Rabbit]

It would help if you told us:
1) What line throws the error.
2) What the string value was at the time of error.

[Frinavale]

What Line?
Have you tried using one of the DateTime.Parse methods?

-Frinny