I have Office 2003, but at work we have Office XP, so my ERP->Outlook project would not run, since it would not find the proper DLL (Microsoft.Office.Interop.Outlook.dll). Now I downloaded the Office XP PIA‘s, and I’ve rebuild the application with these assemblies. The application still works with Office 2003, so I will find out tomorrow if it solved the problem for Office XP.
Update: it works! So the Office 11 .DLL can not be used with Office 10, but the other way around works fine. I would have guessed that backwards compatibility would have taken care of things, but not with MS Office…