This is from a Sametime client issue ... but there could be a similar issue with OCS. Are you using the newest BB OCS client?
| SDR 181474 |
If a user has a large number contacts in the contact list (for example, over 100 contacts in a public folder), the user might receive a “Device has been denied access by the server” error message when logging in. This issue only occurs if the BlackBerry Collaboration Service uses a proxy server.
Restart the BlackBerry Collaboration Service.