OnClick event doesn't fire but OnClientClick does

function Redirect_Final()
{
    display_inner_dropdown(false);
    var Qstring,tid,bid,beid,bdid,r;
    var content;
    document.form1.method="post";
    document.form1.action="Report_Card.aspx";
    content = calculate();
    content += '<br><table align=center cellpadding=1>'
    content += '<tr><td colspan=2 align=left style="color: #FFFFFF; font-family: Arial; font-size: 8pt" bgcolor="#FF0000"><input type=checkbox id=ichk onclick=on_off();> <b>I Accept the above Information.</b> </td></tr>'
    content += '<tr>'
    content += '<td><input id=ibtnsubmit type=button class=mybutton disabled value="Final Submit" onclick=submitMe();></td>'
    content += '<td><input type=button class=mybutton value=Cancel onclick=No_submit();></td>'
    content += '</tr></table>'
    showDialog('Confirmation',content,Global);
}


function submitMe() {

    xmlHttp=ajaxOperation()
    username = document.getElementById("hidusername").value;
    testid = document.getElementById("hidtestid").value;
    str = target + "?type=0&U=" + username + "&T=" + testid;
    sendPage(xmlHttp,str);
    //document.form1.action = "Report_Card.aspx?U=" + username + "&T=" + testid;
    document.form1.submit();
}
function No_submit()
{
    display_inner_dropdown(true)
    hideDialog();
}

<td style="height: 50px; text-align: right">
                                            <asp:Button ID="btn_Submit" OnClientClick="if (!Redirect_Final()) {return false;}" Text=""
                                                runat="server" CssClass="finishnormal" UseSubmitBehavior="False" Height="30px"
                                                Width="94px" onmouseover="this.className='finishhover'" onmouseout="this.className='finishnormal'"
                                                Style="left: 0px" OnClick="btn_Submit_Click" />
                                              
                                        </td>

protected void Load_End_Timer()
{
    sql = "sp_EndTime_New_LMS_Test '" + hidusername.Value + "'," + hidtestid.Value;
    DBCon.Simple_InsUpdDel(sql, 3);
}

protected void btn_Submit_Click(object sender, EventArgs e)
{
    Load_End_Timer();
}