multitasking problem in pic18f26j50

i have a problem in multitasking with pic 18f26j50..Actually only highest priority task is running continuously.preemitive  function is not happening..suppose if i assigned all task with same priority means the last task is running continuously.suppose if i kept different priority means only highest priority task is running continuously.i tried many times i cant find out the problems in it..anyone help me to find out the problem…thank u in advance…

multitasking problem in pic18f26j50

Is your tick interrupt firing/executing? Regards.

multitasking problem in pic18f26j50

actually this is the first time i am programming in rtos can i know how to check tick interrupt is firing/executing….plz help me to know….