String was not recognized as a valid DateTime.

Hi 

I have created web site.it I am passing  datetime in a  page, while saving  I am getting error. 

  Message: Sys.WebForms.PageRequestManagerServerErrorException: String was not recognized as a valid DateTime.

  I have given code below . While updating also i am getting the same eror. Please help me to fix the error.Is the date format different in remote server?

DateTime Datecurrdate = Convert.ToDateTime(DateTime.Now);

DateTime dt2 = Convert.ToDateTime(Datecurrdate);
DateTime dt = Convert.ToDateTime(txtRemindDate.Text);

string strQtyString = "INSERT INTO FOLLOWUPREQUEST(FRFNumber,FRFDate,WorkType,PartyName,"+ " Remarks,RemindDate,RemindMe,RemindOthers,IsCompleted,PreparedBy,PreparedDateTime,BranchCode)"+ " VALUES(" + maxFRFNo + ",'" + Datecurrdate.Date.ToString("yyyy-MM-dd") + "'," + WorkType + ",'" + txtPartyName.Text + "','" + txtRemarks.Text + "',"+ " '" + dt.Date.ToString("yyyy-MM-dd") + "'," + Remainme + "," + RemindOthers + "," + IsCompleted + "," + PrepardBy + ",'" + Datecurrdate.ToString("yyyy-MM-dd H:mm:ss") + "',1001)";

For update the query is

string strQtyString = "Update FOLLOWUPREQUEST set WorkType = " + WorkType + ",PartyName ='" + txtPartyName.Text + "',"+ " Remarks='" + txtRemarks.Text + "',RemindDate='" + rdate.Date.ToString("yyyy-MM-dd") + "',RemindMe =" + Remainme + ","+ " RemindOthers=" + RemindOthers + ",IsCompleted = " + IsCompleted + ",BranchCode=1001 where FRFNumber=" + txtFRFNumber.Text + "";

In aspx page 

<asp:TextBox ID="txtRemindDate" runat="server"></asp:TextBox>
<asp:CalendarExtender ID="cccc" runat="server" TargetControlID="txtRemindDate" Format="dd-MM-yyyy">
</asp:CalendarExtender>
<asp:RequiredFieldValidator ID="RequiredFieldValidator4" runat="server" ControlToValidate="txtRemindDate"
ErrorMessage="cannot be null" ValidationGroup="valSave" SetFocusOnError="true"
CssClass="warning"></asp:RequiredFieldValidator>
 

Thanks

Chandran