Error in date time.....Gridview updating.

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C#

ASP.NET

SQL-Server

DateTime

Hi frnds,

Please can you help me this error.

The conversion of a char data type to a datetime data type resulted in an out-of-range datetime value.
The statement has been terminated.

This code is in Gridview Update Button Click. I have a Update Image Button In Gridview.

In Database I gave Issuedate and ExpiryDate DATATYPE as DateTime.

protected void btnUpdate_Click(object sender, EventArgs e)
   {
       con.Open();

SqlCommand cmd = new SqlCommand("UPDATE AddUsers SET FirstName='" + txtfname.Text + "',LastName='" + txtlname.Text + "',EmpNo='" + txtEmpNo.Text + "',Sponsor='" + txtSponsor.Text + "',ManagerName='" + txtManagerName.Text + "', Dept='" + txtDepartment.Text + "',Location='" + txtLocation.Text + "',OffTelNo='" + txtOffTelNo.Text + "',MobileNo='" + txtMobileNo.Text + "',IssuedDate='" + txtIssueDate.Text + "',ExpiryDate='" + txtExpiryDate.Text + "' Where Id=@Id", con);

cmd.Parameters.AddWithValue("@FirstName", txtfname.Text);
        cmd.Parameters.AddWithValue("@LastName", txtlname.Text);
        cmd.Parameters.AddWithValue("@EmpNo", txtEmpNo.Text);
        cmd.Parameters.AddWithValue("@Sponsor", txtSponsor.Text);
        cmd.Parameters.AddWithValue("@ManagerName", txtManagerName.Text);

        cmd.Parameters.AddWithValue("@Dept", txtDepartment.Text);

        cmd.Parameters.AddWithValue("@Location", txtLocation.Text);

        cmd.Parameters.AddWithValue("@OffTelNo", txtOffTelNo.Text);

        cmd.Parameters.AddWithValue("@MobileNo", txtMobileNo.Text);

        cmd.Parameters.AddWithValue("@IssuedDate", txtIssueDate.Text);

        cmd.Parameters.AddWithValue("@ExpiryDate", txtExpiryDate.Text);
        cmd.Parameters.AddWithValue("@Id", Convert.ToInt32(lblID.Text));

 cmd.ExecuteNonQuery();
        con.Close();

 ScriptManager.RegisterStartupScript(this, this.GetType(), "RunCode", "javascript:alert('Updated successfully');", true);
        BindGV();
}

This is the error am getting when update button click.

The conversion of a char data type to a datetime data type resulted in an out-of-range datetime value.
The statement has been terminated.

Please help. THANKS.