Operation is not valid, because of the current state of the object

Question

I have an Infopath 2010 form with a button and the following event code:

Public Sub txtGetCC_Changing(ByVal sender As Object, ByVal e As XmlChangingEventArgs)
        ' Ensure that the constraint you are enforcing is compatible
        ' with the default value you set for this XML node.

        Dim myNav As XPathNavigator = Me.MainDataSource.CreateNavigator


        If myNav.SelectSingleNode("//my:txtGetCC", Me.NamespaceManager).ToString.Length > 0 Then

            Dim myIterator As XPathNodeIterator = myNav.Select("/my:myFields/my:group11/my:group12", Me.NamespaceManager)
            Dim CCnummer As String = ""
            Dim CCsource As DataSource = Me.DataSources("CostCenters")
            Dim email As String = ""

            While myIterator.MoveNext
                CCnummer = myIterator.Current.SelectSingleNode("my:cbRTcc", Me.NamespaceManager).Value

                Dim myNavigator As XPathNavigator = Me.DataSources("CostCenters").CreateNavigator
                Dim rows As XPathNodeIterator = myNavigator.Select("/dfs:myFields/dfs:dataFields/d:CostCenters", Me.NamespaceManager)

                email = ""
                While (rows.MoveNext)
                    Dim ccnumber As String = rows.Current.SelectSingleNode("@CCnumber", Me.NamespaceManager).Value
                    If ccnumber = CCnummer Then
                        email = rows.Current.SelectSingleNode("@Email", Me.NamespaceManager).Value
                        Exit While
                    End If
                End While
                myIterator.Current.SelectSingleNode("//my:txtCCowner", Me.NamespaceManager).SetValue(email)
            End While
        End If
    End Sub

The line just before the last END WHILE is not working. I want to update the column txtCCowner in the repeating table to be updated with the email address found in the external datasource. Everything works except this line.

The error message I get is: Operation is not valid, because of the current state of the object. Why do I get this error, what am I doing wrong?

Any help is greatly appreciated.

rg. Eric