ASPX.NET RadToolbarButton POSTBACK ISSUE

I have the following

1) ASPX FILE:

<%@ Page Language="VB" AutoEventWireup="false" CodeFile="lastOne.aspx.vb" Inherits="Forms_lastOne" %>
"http://www.w3.org/1999/xhtml">
"server">
"text/javascript">
function OpenWindow(sID, sURL)
{
var oManager = GetRadWindowManager();
oManager.open(sURL, sID);
return false; //
var oWnd = radopen(sURL, sID);
}
function OnClientButtonClickingHandler(sender, eventArgs)
{
alert("aaaaaaaa") //eventArgs.set_cancel(true);
}
"form1" runat="server">
"true" Behaviors="Close, Move" ID="m_oRadWindowManager" runat="server" Modal="true" Skin="Windows7">
"m_oEditLocDialog" VisibleOnPageLoad="false" Title="Edit Location" VisibleStatusbar="false" NavigateUrl="~/Forms/Exports/ExportGrid.aspx" runat="server" Modal="true" Width="550" Height="500">
"server">
"RadScriptManager1" runat="server" />
"m_oEditBtn" Text="EditBtn" runat="server" OnClick="OpenWindow">
"m_oOverviewToolbar" runat="server" Width="100%" EnableRoundedCorners="True" EnableShadows="True" OnButtonClick="m_oOverviewToolbar_ButtonClick" >
"server" Text="OpenRadWindow" CommandName="Edit">
"i1" runat="server" CommandName="View" Text="ShowMsg" PostBack="false" >

2) VB CODE ( Behind Code)

Imports Telerik.Web.UIPartial
Class Forms_lastOne Inherits System.Web.UI.Page
Protected Sub OpenWindow(sender As Object, e As EventArgs)
OpenWindow(Me, m_oEditLocDialog, Nothing)
End Sub
Protected Sub OpenWindow(oParentCtrl As Control, oWindow As RadWindow, sURL As String)
RadScriptManager.RegisterStartupScript(oParentCtrl, oParentCtrl.GetType(), "openWnd", String.Format("OpenWindow('{0}', '{1}');", oWindow.ID, sURL), True)
End Sub
Protected Sub m_oOverviewToolbar_ButtonClick(sender As Object, e As RadToolBarEventArgs) Handles m_oOverviewToolbar.ButtonClick
Dim oBtn As RadToolBarButton = e.Item
If (oBtn.CommandName = "Edit") Then
OpenWindow(Me, m_oEditLocDialog, Nothing)
ElseIf (oBtn.CommandName = "View") Then
MsgBox("OK")
End If
End Sub
End Class

Problem:

When I press in toolbarbutton (view button) its shown message "OK" but when I reload or refresh the page the same message "OK" showing again .

SO how can I prevent any action after reloading or refreshing the page and when I press on Toolbarbutton