Why My Button Click Event Is Not Fired For Server Side Validation And How Could I Do My Server Side Validatio?

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ASP.NET

C#5.0

My button click event is working well when i remove pgae.IsValid() in my code behind.But its not working in the presence of Page.IsValid() because my page.IsValid() always takes False.So my code written in my button click event is not working;
my code are as follows

protected void btnGetDetails_Click(object sender, EventArgs e)
    {
        //to check server side validation if javascript is disabled
        Page.Validate();
       if (Page.IsValid == true)
        { gvEmployeeAttendance.DataSource = empAttendanceService.GetEmployeeAttendanceByDate(employeeID, fromDate, toDate);
            gvEmployeeAttendance.DataBind();
        }

//Code in My .aspx page

<asp:Button ID="btnGetDetails" runat="server" ForeColor="Blue" Text="Get Details" OnClick="btnGetDetails_Click" ValidationGroup="FilterAttendance" />