Unable to cast String to DateTime

Unable to cast String to DateTime

I've following TextBox with ajax calender extender and on TextChanged
event I am calling "txtFromDate_TextChanged" function.
asp code:
<asp:TextBox ID="txtFromDate" runat="server" AutoPostBack="True"
ontextchanged="txtFromDate_TextChanged"></asp:TextBox>
asp:CalendarExtender ID="txtFromDate_CalendarExtender"
Format="dd/MM/yyyy" runat="server" Enabled="True"
TargetControlID="txtFromDate">
</asp:CalendarExtender>
c# code:
protected void txtFromDate_TextChanged(object sender, EventArgs e)
{
if (txtFromDate.Text != "")
{
DateTime fromdate = Convert.ToDateTime(txtFromDate.Text);
Query = Query + "And CONVERT(DATETIME, FLOOR(CONVERT(FLOAT,
ord_del_date))) >= '" + fromdate.ToString("yyyy'-'MM'-'dd") + "'";
}
}
This code is working all fine when i debug through visual studio and even
when I host the site on my local IIS server. The problem is that when I
host the site on my online hosting server and when I pick a date from
calender and calls a textchanged event it gives following error:
Error:
String was not recognized as a valid DateTime.
I know it is giving error because of line:
DateTime fromdate = Convert.ToDateTime(txtFromDate.Text);
But I am not finding anything wrong in this code. This code is working
perfectly fine from visual studio or when hosted on IIS but I am totally
confused why it isn't working when hosted on hosting server. I am totally
confused. Please help me out.