Using older BlackBerry devices, it is not possible to load the Service Desk Manager PDA interface. Using newer devices works fine.
If you are using IIS 7.5 or IIS 8, please check whether IIS - Windows Authentication (or other method) is enabled.
Try disabling it or changing to "Basic Authentication" or "Anonymous" and test to see if it loads.
Older versions of the BlackBerry Operating System do not support all IIS Authentication methods.
This is a limitation in older releases of BB OS.