It happens opening every old scene (viz 2005) using a previous version of your plugin but only if the workspace is changed from its default state (ex. moving or docking toolbars an so on); I know it seems funny but that exactly what is happening here! Returning to default state deleting vizstartui.cui seems to be a reliable workaround but it's annoying.
I can say that it's a quite fresh system; I mean not many SW running and only CC and VRay as VIZ plugins. I was slowy testing everything and doing so I found that issue. At first sight I thought it was a VIZ issue but trying to create a simple test scene in VIZ 2005 with no CC texture applied I realized that the issue in VIZ 2008 was gone; so unintalled CC from VIZ 2008 and so far everything it's running fine.