Nope, you are missing the Administer Information Store permission more than likely. It's the one that allows the rights to create entries/folders in the mailbox. Check
ALL permissions down to the mailbox store and public folder store in the Exchange System Manager using this article:
BlackBerry Search Results
One of 2 things is happening:
1. Either permissions are set incorrectly
2. Or they have not written to the mailbox and therefore do not work
Check them again and if you are confident they are correct it's the account itself. The best solution is to create another BESAdmin and try again.
Let us know what fixes it.