The New Hire coverage start date formula is giving error on evaluation

Summary:

We have a requirement where the coverage for part timers should start after 1 year through New Hire life event.

We tried to achieve it using the below formula but are receiving error on evaluating the life event.

Default for PER_PER_LATEST_REHIRE_DATE is '1951/01/01 00:00:00'(date) 

DEFAULT FOR PER_WORKER_ASSIGNMENT_FULL_PART_TIME IS 'FULL_TIME' 

L_OCRD_DT = PER_PER_LATEST_REHIRE_DATE 

L_PART = PER_WORKER_ASSIGNMENT_FULL_PART_TIME 

IF L_PART = 'PART_TIME' THEN    
(
l_start_dt = ADD_DAYS(LAST_DAY(add_months(L_OCRD_DT,12)), 1)
)

ELSE 
(
l_start_dt = L_OCRD_DT