I got it! You must use CommandManager instead of just SaveAs...
Call oApp.CommandManager.PostPrivateEvent(kFileNameEvent, "C:\kn300.dxf")
Call oApp.CommandManager.StartCommand(kFileSaveCopyAsCommand)
It worked very well in Inventor 7, so I decided to move to a computer that has IV8 and all I could get from Autodesk Inventor is "Unhandled Exception" or the same old error boxes...so who can explain that???
Thanks!
FOP