Error in COM Microsoft.Office.Interop

[ayaxrm]

I have an application made in .net. This program link with formfields in word application. This is the code:

Dim wdApp As Object
Dim wdDoc As New Word.Document
Dim strLabelName = ruta + "\oferta.dot"

wdApp = CreateObject("Word.Application")
wdApp.Visible = True
wdDoc = wdApp.Documents.Add(strLabelName)

With wdDoc

.FormFields("txt_oferta").Result = oferta

.FormFields("txt_nombre").Result = nombre

end with

In all computers of my enterprise, work perfectly but, in the manager's computer doesn't work, bad luck . The program run well, but fails when it arrives the line ".FormFields("txt_oferta").Result = oferta".

the error is
Unable to cast COM object of type
'Microsoft.Office.Interop.Word.DocumentClass' to interface type
'Microsoft.Office.Interop.Word._Document'. This operation failed because the
QueryInterface call on the COM component for the interface with IID
'{0002096B-0000-0000-C000-000000000046}' failed due to the following error:
The application called an interface that was marshalled for a different
thread. (Exception from HRESULT: 0x80004002 (E_NOINTERFACE)).

I installed microsoft office 2003 primary interop assemblies but it doesn't work.

any ideas?

I'm a little bit desperate.

thank you very much.