iCal and Exchange 2010

I have a user whos iCal is not syncing with Exchange 2010. When creating a new event, it gives the message "iCal can't save the event "xxxx" to the Exchange server. The account "xxxx" currently can't be modified. To discard your changes and continue using the version of your calendars that's on the server, click Revert to Server. To save your changes on your computer until the problem is resolved, click Go Offline."

The user is on a 2011 13" Macbook Air, 1.86 GHz Core 2 Duo. Snow Leopard 10.6.7, iCal 4.0.4. Mail and Address Book sync fine. The calendar works fine from the users iPhone, Outlook Web Access, and Outlook 2011 on the computer.

I have tried deleting the account, deleting all caches, and recreating it, but it still doesn't work. I made sure Tasks weren't the problem, and checked time zone support as well.

I set up the exchange account on my Macbook and it works fine, no problems syncing over wired or wireless connections. Macbook is also on 10.6.7, iCal 4.0.4. So I was thinking it was a user account issue. I created a new account on the Macbook Air, set up the exchange account in iCal, and I get the same problem as on the original account, no syncing.. I have everything set up exactly the same as on my Macbook, but the Macbook Air refuses to sync. This error only appears when an event created on the Macbook Air is in the calendar. It pulls events from the server fine, but once an event is created it refuses to cooperate.

Do Macbook Airs just not play nice with Exchange?