Oh, well.
I had the same issue as you did using 'Notes.NotesSession'. It would C5 when I typed 'Notes.' in the command window. Switching to 'Lotus.NotesSession' fixed it for me. I'm afraid I don't have another answer.
Sorry,
Alan
>>Cindy, try
oSession = CreateObject('Lotus.NotesSession')
>
>Error: Class definition LOTUS.NOTESSESSION is not found.