Not too sure. But the Fields collection object has a Locked = True/False property which may prevent updating. It also has an Update function to force updates.

So you might try:
[vba]ActiveDocument.Fields.Locked = True
Application.ScreenUpdating = False[/vba]
at the start, and:
[vba]ActiveDocument.Fields.Locked = False
if ActiveDocument.Fields.Update = 0 then
Msgbox "Updates complete"
else
Msgbox "Updates failed to complete."
end if
Application.ScreenUpdating=True[/vba]
at the end.
Note though that I don't do much with Word VBA, and have not tested this code. Maybe someone else can give you a better reply.