error message .... Method Requery of object '_SubForm' failed

I have suddenly started to get an error that crashes me right out of access! ..." Method Requery of object '_SubForm' failed" .

I have an Access 2000 database (running on Access 2003 SP1) that has a form (single form view) with 2 sub forms.  

The main form Topics (based on table tblTopics fields: topicID[key], topic, etc), there is an embedded subform sfCorr (based on table tblCorr with fields: topicID, corrID[key], corr, etc) and another subform sfAction (based on tblActs - fields, ActID[key], TopicID, CorrID, Action etc)

There is one to many relationship between tblTopics and tblCorr based on field TopicID, and one to many relationship between tblCorr and tblActs based on CorrID.

The forms worked OK until I entered a lookup combo on the form to quickly find Topic. Code below...  The error comes when the combo is used to move to a new topic.

Private Sub ComboTopicFind_AfterUpdate()
    ' Find the record that matches the control.
    Dim rs As Object

    Set rs = Me.Recordset.Clone
    rs.FindFirst "[TopicID] = " & Str(Me![ComboTopicFind])
    Me.Bookmark = rs.Bookmark
End Sub

The subform sfCorr has a OnCurrent piece of code so that the subform sfAct choses the relevent records.

Private Sub Form_Current()
    Dim strParentDocName As String

    On Error Resume Next
    strParentDocName = Me.Parent.Name

    If Err <> 0 Then
        GoTo Form_Current_Exit
    Else
        On Error GoTo Form_Current_Err
        Me.Parent![sfAction].Requery
    End If

Form_Current_Exit:
    Exit Sub

Form_Current_Err:
    MsgBox Err.Description
    Resume Form_Current_Exit
End Sub

(This is the only incidence of the Requery in the whole project).  I've tried recreating combo and get no difference, have also tried repair, compact.