You must make sure you have added a construction to your schedule before attempting to add a work item. A construction will look like an orange square. Scheduler KB10041-01
  1.     Click on the desired work item (white and blue icon), by clicking and holding the mouse button down. Scheduler KB10041-02
  2.     Move the pointer over to the construction that you want the work item to be placed under
  3.     Release the mouse button, this will drop the work item into this heading.

Scheduler KB10041-03