Background tasks (PC programs) are mostly keep each other alive. In some cases there's a so called "watchdog task" that checks if another task is running and if not restarts that task. In the template file "KRG" of the K-IDE you'll find such a watchdog task in "autostart5.pc".
Watchdog tasks makes it a bit more difficult to kill other tasks after changing a pc program and before upload. In some cases it may happen, that the watchdog task restarts a task that is just killed and before the new pc program is transferred. Therefore the watchdog task has to be killed before the task of the pc program you like to upload to the robot.
In K-IDE the default order to kill a task is from one to five. For a project made out of the template "KRG" for example the kill order may make trouble. For that reason task 5 has to be killed before the other tasks. You can change the order of the tasks to be killed by simply drag and drop the tasks in all dialog boxes that present the tasks to be killed. For a project like the KRG template you may want to change the order that task 5 is the first task to be killed.