Sometimes the problems administrators run into with BES are simply due to improper permissions. The besadmin account (the BlackBerry administrator account) requires certain permissions to do it’s job correctly.
More often than not we find out that someone has been mucking around with the permissions or they just weren’t set correctly in the first place and this causes an issue with BlackBerry devices sending and receiving e-mail.
BlackBerry has some nice directions on their web site on how to setup the appropriate permissions. You can find them here.