Daishi or whatever has the resolution posted above (Just verified it on my server). Basically, what you need to do is verify on the Blackberry user in question if, under their mailbox rights, your BES Admin has Full Mailbox Access under the 'Exchange Advanced', 'Mailbox Rights'. If your BES admin does not, it will not have rights to the mailbox to create Calendar objects, despite being able to sync Contacts, Mail and other items. The resolution posted above is basically stating that the BES Admin account should be given both 'Receive As' and 'Send As' on the Exchange System Manager for the particular server which should also have 'Allow inheritable permissions from parent to propagate to this object' to shuffle it down to all your Blackberry Users.

The short, quick and dirty way to do this is to go to every Blackberry user in your Active Directory and go into the 'Exchange Advanced', 'Mailbox Rights' and grant the BES Admin 'Full mailbox access' for it to work.