Webbrowser Session maintaining problem

I have created an application for automated form filling in a website.Basically i have to through 2 pages Login page and then the form filling page.Instead of going through two different pages,two times,I have prefered navigating the second page itself.That way if i am not logged in, the login page automatically comes up and then after filling in my credentials it auto redirects me to my page.

Now the problem is sometimes some sites dont redirect,so to deal with it I kept a timer for this purpose.After 6 secs after the login page I forcibly navigate to the second page via wb.navigate("http://abc.com/page2.htm")

Sometimes randomly,it again takes me to the login page although it previously shows I am logged in.....

I tried finding the solution to this but everywhere i found some answers of how to maintain session between 2 new windows.I have only ONE IE mshtml WEBBROWSER I am navigating all sites through that.

Now what could be the problem???
It seems as if the session is breaking when i forcibly navigate the second time,even though i am using one webbrowser.Moreover sometimes it works,sometime it doesnt :(

Part of my code

VB2008 Code:

wb.Navigate(CPath)                      '1st  page navigation
 
WaitTillLoad()
 
If LoginPresent Or LoginPresent1 Or LoginPresent2 Or LoginPresent3 Then
                        DirectCast(GetCurrentWebForm(index1).item(Username), mshtml.HTMLInputElement).value = TextBox1.Text
                        DirectCast(GetCurrentWebForm(index1).item(Password), mshtml.HTMLInputElement).value = TextBox2.Text
                        If RememberMe <> "" Then
                            DirectCast(GetCurrentWebForm(index1).item(RememberMe, 0), mshtml.HTMLOptionButtonElement).checked = True
                        End If
                        If Login <> "" Then
                            DirectCast(GetCurrentWebForm(index1).item(Login, 0), mshtml.HTMLButtonElement).click()
                        Else
                            GetCurrentWebForm(index1).submit()
                        End If
 
 
                        pause(5000)                                 'Waiting 5secs to redirect
                        wb.Navigate(CPath)           'Redirecting to 2nd page forcibly irrespective it redirected succesfully or not
                        WaitTillLoad()
                    End If

Anyone has better logic,please contribute