To enable Automatic Wireless Backup on BlackBerry Enterprise Server 5.0, complete the following steps:

In the BlackBerry Administration Service, select Users > Manage Users.
On the Manage Users tab, click a BlackBerry smartphone user account.
Click Default Configuration under Messaging configuration.
Click Organizer data synchronization.
Click Edit User.
In the drop-down list for Automatic Wireless Backup Enabled, click True.
Click Continue to user information edit.
Click Save all.
After that activate user again.