The asynchronous operation has already completed - vb.net

Question

I have a VB.net app with a DataGridView displaying a list of jobs, retrieved from a SQL query into a DataTable, then a DataView and finally a BindingSource for the DataGridView.DataSource. I have recently added SqlNotificationRequest functionality to the setup so user A is immediately updated when user B performs an action on a job in the list.
I used this MSDN article (http://msdn.microsoft.com/en-US/library/3ht3391b(v=vs.80).aspx) as the basis for my development and it works ok. The problem comes when the user wants to change the parameters of the SQL query which displays the jobs, for example the date displayed. Currently I am creating a new SqlCommand with new Notification but after the user has changed the date a few times (say 30), but no data changes, when the notification timeout occurs I receive the above error when the callback handler tried to EndExecuteReader. My callback handler is below:
Private Sub OnSalesReaderComplete(ByVal asynResult As IAsyncResult)
' You may not interact with the form and its contents
' from a different thread, and this callback procedure
' is all but guaranteed to be running from a different thread
' than the form. Therefore you cannot simply call code that
' updates the UI.
' Instead, you must call the procedure from the form's thread.
' This code will use recursion to switch from the thread pool
' to the UI thread.
If Me.InvokeRequired Then
myStatus.addHistory("OnSalesReaderComplete - Background", "Sub")
Dim switchThreads As New AsyncCallback(AddressOf Me.OnSalesReaderComplete)
Dim args() As Object = {asynResult}
Me.BeginInvoke(switchThreads, args)
Exit Sub
End If
' At this point, this code will run on the UI thread.
Try
myStatus.addHistory("OnSalesReaderComplete - UI", "Sub")
Dim sourceText, rSalesId As String
waitInProgressSales = False
Trace.WriteLine(String.Format("Sales:asynResult.IsCompleted1: {0}", asynResult.IsCompleted.ToString), "SqlNotificationRequest")
Trace.WriteLine(String.Format("Sales:asynResult.CompletedSynchronously: {0}", asynResult.CompletedSynchronously.ToString), "SqlNotificationRequest")
Dim reader As SqlDataReader = DirectCast(asynResult.AsyncState, SqlCommand).EndExecuteReader(asynResult)
Trace.WriteLine(String.Format("Sales:asynResult.IsCompleted2: {0}", asynResult.IsCompleted.ToString), "SqlNotificationRequest")
Do While reader.Read
' Empty queue of messages.
' Application logic could parse
' the queue data to determine why things.
'For i As Integer = 0 To reader.FieldCount - 1
' 'Debug.WriteLine(reader(i).ToString())
' Console.WriteLine(reader(i).ToString)
'Next
Dim bytesQN As SqlBytes = reader.GetSqlBytes(reader.GetOrdinal("message_body"))
Dim rdrXml As XmlReader = New XmlTextReader(bytesQN.Stream)
Do While rdrXml.Read
Select Case rdrXml.NodeType
Case XmlNodeType.Element
Select Case rdrXml.LocalName
Case "QueryNotification"
sourceText = rdrXml.GetAttribute("source")
Case "Message"
rSalesId = rdrXml.ReadElementContentAsString
End Select
End Select
Loop
Loop
reader.Close()
' The user can decide to request
' a new notification by
' checking the check box on the form.
' However, if the user has requested to
' exit, we need to do that instead.
If exitRequestedSales Then
'Me.Close()
commandSales.Notification = Nothing
Else
Select Case sourceText.ToLower
Case "data"
Trace.WriteLine(String.Format("SalesId: {0}, data notification", rSalesId), "SqlNotificationRequest")
Call GetSalesData(True, action.REATTACH)
Case "timeout"
'check timeout is for this user and relates to current wait thread
Select Case salesId = rSalesId
Case True
Trace.WriteLine(String.Format("SalesId: {0}, timeout - current", rSalesId), "SqlNotificationRequest")
Call GetSalesData(True, False)
Case False
Trace.WriteLine(String.Format("SalesId: {0}, timeout - old", rSalesId), "SqlNotificationRequest")
Me.ListenSales()
End Select
End Select
End If
Catch ex As Exception
Call errorHandling(ex, "OnSalesReaderComplete", "Sub")
End Try
End Sub
The problem seems to be where I am only refreshing the data and renewing the notification request (using GetSalesData) when either the notification is due to an update ("data") or the timeout is for the current request. On other notifications, the application calls Me.ListenSales which creates a SQL command "WAITFOR (RECEIVE * FROM [QueueMessage])" and starts the callback listener as per the MSDN article. If I remove the Me.ListenSales line, once a notification is received which is not due to data or the timeout of the current query, the application stops listening for notifications.
I have also posted the same question on MSDN forums (http://social.msdn.microsoft.com/Forums/en-US/adodotnetdataproviders/thread/0f7a636d-0c9b-4b39-b341-6becf13873dc) as I have tried other resolutions without success so require some advice on whether this is possible and if so how.