Closing a new document with textvariable

1. In Indesign CS4 version 6.0.2 ,

if I create a new document and insert a textvariable, I can save the document and I can close it.

2. In scripting Indesign CS4 version 6.0.2 with VB.net (Visual Studio 2008 + Framework 3.5),

if I open a document manually created under Indesign CS4 version 6.0.2 with a textvariable, I can save the document and I can close it.

3. In scripting Indesign CS4 version 6.0.2 with VB.net (Visual Studio 2008 + Framework 3.5),

if I create a new document and insert a textvariable, I can save the document, but I can't close it. Indesign give a win32 error.

MyPub = myIndesign.Documents.Add(False)

MySpread = MyPub.Spreads.Item(1)
myTextFrames = MySpread.TextFrames
MyInfos = myTextFrames.Add

Dim FileNameVariable As InDesign.TextVariable = Nothing

For Each Item As TextVariable In MyPub.TextVariables
      If Item.VariableType = idVariableTypes.idFileNameType Then
               FileNameVariable = Item
               Exit For
     End If
Next
Dim FileNameVariableInstance As InDesign.TextVariableInstance = Nothing
FileNameVariableInstance = MyInfos.TextVariableInstances.Add(idLocationOptions.idAtBeginning)
FileNameVariableInstance.AssociatedTextVariable = FileNameVariable

MyPub.Save(FullPath)   'OK

MyPub.close               'Error Win32 in Indesign.exe

I try to save the document before creating the FileNameVariableInstance but it's the same result.

Do you know a way to do it ?