When I try to delete an instance of a recurring event on Outlook, it would not synchronize with the Blackberry (So the entry on outlook is gone, but not the one on Blackberry). It will not sync by wired or by wireless.

I am using the latest desktop software / firmware. But not sure about BES version

Do you have your conflict/change options set correctly??

In other words when syncing you can choose whether or no to be prompted for changes or conflicts..