[Solved] ASP.Net GridView OnSelectedIndexChanged Error: String was not recognized as a valid DateTime

String was not recognized as a valid DateTime on selected indexchange of gridview

below refere your provided solution Set TextMode Date value on GridView row selection using C# and VB.Net in ASP.Net

Now i define column in gridivew 

                        <asp:GridView ID="gvv" runat="server" AutoGenerateSelectButton="true" AutoGenerateColumns="false" OnSelectedIndexChanged="gvv_SelectedIndexChanged" BackColor="White" BorderColor="#3366CC" BorderStyle="None" BorderWidth="1px" CellPadding="4">
                            <FooterStyle BackColor="#99CCCC" ForeColor="#003399" />
                            <HeaderStyle BackColor="#003399" Font-Bold="True" ForeColor="#CCCCFF" />
                            <PagerStyle BackColor="#99CCCC" ForeColor="#003399" HorizontalAlign="Left" />
                            <RowStyle BackColor="White" ForeColor="#003399" />
                            <SelectedRowStyle BackColor="#009999" Font-Bold="True" ForeColor="#CCFF99" />
                            <SortedAscendingCellStyle BackColor="#EDF6F6" />
                            <SortedAscendingHeaderStyle BackColor="#0D4AC4" />
                            <SortedDescendingCellStyle BackColor="#D6DFDF" />
                            <SortedDescendingHeaderStyle BackColor="#002876" />
                            <Columns>
                               <asp:TemplateField HeaderText="ID">
                                                                  <ItemTemplate>
                                                                      <asp:label ID="lbid"  runat="server" Text='<%#Bind("ID")%>'></asp:label>
                                                                  </ItemTemplate>
                                                              </asp:TemplateField> 
                                   <asp:TemplateField HeaderText="Name">
                                                                  <ItemTemplate>
                                                                      <asp:label ID="lbname"  runat="server" Text='<%#Bind("Name")%>'></asp:label>
                                                                  </ItemTemplate>
                                                              </asp:TemplateField> 
                                  <asp:TemplateField HeaderText="Designation">
                                                                  <ItemTemplate>
                                                                      <asp:label ID="lbdesignation"  runat="server" Text='<%#Bind("designation")%>'></asp:label>
                                                                  </ItemTemplate>
                                                              </asp:TemplateField> 
                                 <asp:TemplateField HeaderText="Joining_Date">
                                                                  <ItemTemplate>
                                                                      <asp:label ID="lbDOJ"  runat="server"  Text='<%# Eval("DOJ", "{0:MM/dd/yyyy}") %>' ></asp:label>
                                                                  </ItemTemplate>
                                                              </asp:TemplateField> 
                                 <asp:TemplateField HeaderText="Salary">
                                                                  <ItemTemplate>
                                                                      <asp:label ID="lbsalary"  runat="server" Text='<%#Bind("salary")%>'></asp:label>
                                                                  </ItemTemplate>
                                                              </asp:TemplateField> 
                             </Columns>
                         </asp:GridView>

      protected void gvv_SelectedIndexChanged(object sender, EventArgs e)
      {
          lblastid.Text = gvv.SelectedRow.Cells[1].Text;
          txtname.Text = gvv.SelectedRow.Cells[2].Text;
          txtsalary.Text = gvv.SelectedRow.Cells[3].Text;
          txtdoj.Text = Convert.ToDateTime(gvv.SelectedRow.Cells[5].Text).ToString("dd/MM/yyyy");
          string des = gvv.SelectedRow.Cells[4].Text.Trim().Replace(" ", "");
          txtdeduction.Text = gvv.SelectedRow.Cells[6].Text.Trim().Replace(" ", "");
          ddldesignation.ClearSelection();
          if (ddldesignation.Items.FindByText(des) != null)
          {
              //  DDUOM.Items.FindByText(gvv.SelectedRow.Cells[4].Text).Selected = true;
              ddldesignation.Items.FindByText(des).Selected = true;
          }