Show all the tasks across all created Programs to which the resource is assigned.
The tasks originating from other Programs are partially transparent and you will not be able to move them using drag and drop. Such tasks update the resources' workload (allocation).
Viewing tasks from all Programs' is a BigPicture Enterprise feature.
Resources module has an option to show allocation across all Programs using the Show overall assignment from all programs option from the View menu. This option concerns Global Teams only, so to use it, you need to use Global Teams in more than one Program and assign tasks to these teams in those programs.