To load applications using Desktop Manager, the version of the Desktop Manager must match the O/S version installed on your Blackberry. Please refer to the followings on how to check their versions.

If they do not match, you have to contact your device provider for a same or newer version of Desktop Manager (newer version will refresh the O/S on your Blackberry) for your device model

To view the O/S version installed on your Blackberry, go: Blackberry Home Screen -> Options (or Settings) -> About

To view the version(s) of the Desktop Manager: Desktop Manager Home Screen -> Help -> About Then change the tab to Device Software.