If Entourage will not sync the Calendar and Contacts try the following steps:

1) In Entourage, right click (or control click) the Contacts folder then choose Folder Properties.
There is a button for "Empty". This will remove the local cache on your Mac for that folder. Before choosing this be sure that you have documented any unsynchronized Contacts. Give it a few minutes to sync back up, then try to add a Contact in Entourage. Wait a few minutes and see if the Contact shows in Outlook Web Access. It can take up to 5 minutes. You can do this same process for the Calendar.

2) If #1 does not work, verify that you have ample disk space on your Mac. If you do, then create a new Identity in Entourage (which is basically like starting over with a new email profile. You can create a new Identity by choosing Entourage, Switch Identity.