Why does the Process Status Viewer show "Recipient Not Found"?

The Process Status Viewer shows "Recipient Not Found" when it is unable to find the employee or external user to whom the task or notification is to be delivered. The various cases for its occurrence are:

• The field by which the employee is being identified is not specified.
• There is no employee present in the selected department.
• The field by which the department is identified to get the employee is not specified.
• The employee to whom the selected employee is reporting to not specified.