The objects in the catalog system can now be programmed in two modes. In the first mode the catalog server assembly is loaded in the callers appdomain (aka inproc mode). In the second mode the functionality of the catalog system is available remotely...

I have seen a few customers hit this issue in the newsgroups. If you are using Windows XP as your development environment for Commerce Server 2007 Developer Edition and importing a catalog gives you an error "Value does not fall within the expected range...