asyncronous methods in asp.net 1.1

Hey

I have a question regarding a problem with binding a async resultset to a
datagrid.

I have a sync function searchproducts, which i want to expose async.
It returns a custom collection object, but I get a object ref exception.....

my class:
-----------------------------------------------------------------

Private Delegate Function InvokeSearchProducts(ByVal searchString As String)
As ProductCollection
Private _deleg As InvokeSearchProducts
Private _ar As IAsyncResult
Private _canceled As Boolean

Public Function SyncSearchProducts(ByVal search As String) As
ProductCollection
'code............
End Function

Public Sub BeginSearchProducts(ByVal searchString As String)
      _deleg = New InvokeSearchProducts(AddressOf SyncSearchProducts)
      _ar = _deleg.BeginInvoke(searchString, Nothing, Nothing)
End Sub

Public Function EndSearchProducts() As Model.ProductCollection
  If _canceled OrElse _deleg Is Nothing Then
      Return Nothing
  Else
      Return _deleg.EndInvoke(_ar)
End If
End Function

-----------------------------------------------------------------

Can anyone help me with this?

Hope hearing from you

Greetings

dotdonk