Trouble adding delegate to Mac Calendar

I have to give my secretary access to my Mac Calendar I have on my MBP. Both she and I are on Exchange (she uses Outlook). When I get to the screen for adding a delegate, it asks for the Name. This is where I am confused. Regardless of whether I enter her name or e-mail address, I get an error that she could not be found on the Exchange server. In fact, I tried putting in my name and it said I couldn't be found. I assumed that when I enter the name, it would search the server and display all matches (like it does with LDAP), but no matter what I enter, I get the same error message about not being found on the server.

I know my Calendar account on Exchange is working, because I get notifications about events on my iPad although I entered the event on my MBP. I am using Mountain Lion.

Thanks for any help.

Subbu