unhandles exception error when login page idle - asp.net

Question

I have developed a site in vb.net (with some help from my brother in law) and it's almost ready to roll out except I am getting an unhandled exception error on the login
screen when the page is idle for a few minutes. I am reasonably new to vb.net and not a programmer :( Any help would be really appreciated. Sorry if anything in my post is not to the site standard as this is my first post. :)
I'm not sure why this is happening. The code that is executed on login_buttonClick is:
Protected Sub LoginWizard_FinishButtonClick(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.WizardNavigationEventArgs) Handles LoginWizard.FinishButtonClick
Dim oUsername As String = txtUsername.Text
Dim oPassword As String = txtPassword.Text
Dim oPath As String = Server.MapPath("App_Data/IOFR.mdb")
Dim oValid As Boolean = False
Dim oReader As System.Data.OleDb.OleDbDataReader = Nothing
Dim oConnection As System.Data.OleDb.OleDbConnection = Nothing
Dim oName As String = ""
Dim oOrg As String = ""
Dim oUserId As Integer = 0
Dim oActiveAcc As String = ""
Dim oSessionExpire As Integer = 0
Try
oConnection = New System.Data.OleDb.OleDbConnection(String.Format("Provider=Microsoft.Jet.OLEDB.4.0; Data Source={0}; Jet OLEDB:Database Password=EdmundColin13", oPath))
oConnection.Open()
Dim ipAddress As String = Request.ServerVariables("REMOTE_ADDR")
Dim cmd As New SqlCommand
Dim oParams As New List(Of System.Data.OleDb.OleDbParameter)
oParams.Add(New System.Data.OleDb.OleDbParameter("#pmUsername", oUsername))
oParams.Add(New System.Data.OleDb.OleDbParameter("#pmPassowrd", oPassword))
Dim oCommand As New System.Data.OleDb.OleDbCommand("SELECT ID, [Name], Organisation, ActiveAccount, [Password] FROM Users WHERE [Username] = #pmUsername AND [Password] = #pmPassword", oConnection)
oCommand.Parameters.AddRange(oParams.ToArray)
oReader = oCommand.ExecuteReader()
If oReader.Read() Then
oValid = True
oName = oReader.GetString(oReader.GetOrdinal("Name"))
oActiveAcc = oReader.GetString(oReader.GetOrdinal("ActiveAccount"))
oOrg = oReader.GetString(oReader.GetOrdinal("Organisation"))
oPassword = oReader.GetString(oReader.GetOrdinal("Password"))
oUserId = oReader.GetInt32(oReader.GetOrdinal("ID"))
oSessionExpire = oReader.GetInt32(oReader.GetOrdinal("SessionExpire"))
End If
Catch ex As Exception
Finally
If Not oReader Is Nothing Then
If Not oReader.IsClosed Then
oReader.Close()
End If
oReader = Nothing
End If
End Try
If oValid And Not String.Equals(txtPassword.Text, oPassword) Then
oValid = False
End If
If oValid Then
If oActiveAcc = "No" Then
Response.Redirect("~/DisabledAccount.aspx")
Return
End If
Session("username") = txtUsername.Text
Session("name") = oName
Session("org") = oOrg
'Generate session id and store it in session
Dim uniquesessionid As String = Guid.NewGuid().ToString()
Session("uid") = uniquesessionid
Dim oCommandSession As New System.Data.OleDb.OleDbCommand("UPDATE Users SET SessionId = #pmid, SessionExpire = '" & DateTime.Now.AddHours(2).ToString() & "' WHERE [ID] = #pmUserid", oConnection)
oCommandSession.Parameters.Add(New System.Data.OleDb.OleDbParameter("#pmid", uniquesessionid))
oCommandSession.Parameters.Add(New System.Data.OleDb.OleDbParameter("#pmUserid", oUserId))
oCommandSession.ExecuteNonQuery()
Response.Redirect("~/Home.aspx?login=true")
Else
txtUsername.BorderColor = Drawing.Color.Red
txtUsername.BackColor = Drawing.Color.Red
txtPassword.BorderColor = Drawing.Color.Red
FailedLogin.Visible = True
End If
If Not oConnection Is Nothing Then
If oConnection.State = Data.ConnectionState.Open Then
oConnection.Close()
End If
End If
End Sub

Answer 1

Thanks All. This seams to have resolved the issue.
EnableViewStateMAC="False"