Exchange 5, Lotus Notes and MAPI

I had Exchange 4, which worked fine with Lotus Notes. Since installation of Exchange 5, I no longer have MAPI capability. If I try to use the mailto: function I get error messages. I even get those messages when I start Exchange via the Mail iconin Control Panel. Specifially the messages are: 1) Logon Session: Can’t Read Password Information; 2) Microsoft Exchange: The set of folders could not be opened. The information store could not be opened. I’ve never used a password. Reinstalled Notes. Now, I get several “Notes Init Failure” messages, with a status code of 1a5. Then the message that MAPI was unable to load the info service nwnsp.dll. Any ideas?