Invalid case exception - linq

Question

In report page i have dropdown and datepicker fromdate and todate and button
so when i select values from dropdown and datepicker then this show error
on this line
dt=report(Convert.ToDateTime(fromdate), Convert.ToDateTime(todate), Convert.ToString(DropDownList1.SelectedValue));
error
An exception of type 'System.InvalidCastException' occurred in mscorlib.dll but was not handled in user code
Additional information: Unable to cast object of type 'System.Web.UI.HtmlControls.HtmlInputText' to type 'System.IConvertible'
.
code
protected void Button1_Click(object sender, EventArgs e)
{
dt=report(Convert.ToDateTime(fromdate), Convert.ToDateTime(todate), Convert.ToString(DropDownList1.SelectedValue));
GridView1.DataSource = dt;
GridView1.DataBind();
}
DataTable dt = new DataTable();
public DataTable report(DateTime fromdate,DateTime todate,string IMEI)
{
DateTime fromdatee = Convert.ToDateTime(Request.Form["fromdate"]);
DateTime todatee = Convert.ToDateTime(Request.Form["todate"]);
Entities track = new Entities();
DateTime fr_date = new DateTime(fromdatee.Year, fromdatee.Month, fromdatee.Day, 0, 0, 0);
DateTime t_date = new DateTime(todatee.Year, todatee.Month, todatee.Day, 23, 59, 59);
List<spGetReport_Result> report = track.spGetReport(IMEI,fr_date,t_date).ToList();
dt.Columns.Add("Time",typeof(DateTime));
dt.Columns.Add("X",typeof(float));
dt.Columns.Add("valuenumber",typeof(int));
foreach(var c in report)
{
dt.Rows.Add(c.Time, c.X, c.valuenumber);
}
return dt;
}
HTML
<form id="form1" runat="server">
<div>
<span>
<asp:DropDownList ID="DropDownList1" runat="server"></asp:DropDownList>
</span>
<span>
<input id="fromdate" runat="server" clientidmode="static" />
</span>
<span>
<input id="todate" runat="server" clientidmode="static" />
</span>
<span>
<asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click" />
</span><br />
<asp:Label ID="Label1" style="margin-left: 220px;" runat="server" Text="Export to"></asp:Label>
<asp:GridView ID="GridView1" runat="server" class="display nowrap"
Width="100%" CellPadding="0"
Font-Names="Verdana" BackColor ="White" BorderColor="#CCCCCC" BorderStyle="None"
BorderWidth="1px" Font-Size="9pt">
<FooterStyle BackColor="White" ForeColor="#000066" />
<HeaderStyle BackColor="#006699" Font-Bold="True" ForeColor="White" />
<PagerStyle BackColor="White" ForeColor="#000066" HorizontalAlign="Left" />
<RowStyle ForeColor="#000066" />
<SelectedRowStyle BackColor="#669999" Font-Bold="True" ForeColor="White" />
<SortedAscendingCellStyle BackColor="#F1F1F1" />
<SortedAscendingHeaderStyle BackColor="#007DBB" />
<SortedDescendingCellStyle BackColor="#CAC9C9" />
<SortedDescendingHeaderStyle BackColor="#00547E" />
</asp:GridView>
</div>
</form>

Answer 1

Because you are sending Convert.ToDateTime the HTML control instead of the string to be converted.
You should be doing this:
dt = report(Convert.ToDateTime(fromdate.Value), Convert.ToDateTime(todate.Value), DropDownList1.SelectedValue);
A very simple debugging process would have quickly showed you where the problem was.
DropDownList1.SelectedValue is already a string, so no point in converting it.
Anyway, you should check first that what's in those inputs are really valid DateTime representations by using a validator.