The new hire coverage start date formula is giving error while evaluating

We are getting the following error while evaluating the new hire event -

We are using the following formula and are unable to troubleshoot -

DEFAULT FOR PER_REL_ORIGINAL_DATE_OF_HIRE is '1951/01/01 00:00:00'(date)
DEFAULT FOR PER_PER_LATEST_REHIRE_DATE is '1951/01/01 00:00:00'(date)
DEFAULT FOR ACP_HIRE_DATE is '1951/01/01 00:00:00'(date)

l_asg_id = GET_CONTEXT(HR_ASSIGNMENT_ID,0)
l_effective_date = GET_CONTEXT(EFFECTIVE_DATE, to_date('1951/01/01 00:00:00'))

l_hire_date = PER_PER_LATEST_REHIRE_DATE

if (PER_PER_LATEST_REHIRE_DATE WAS DEFAULTED) then
(
l_hire_date =ACP_HIRE_DATE
)

L_TEMP = ESS_LOG_WRITE('log start ************ l_hire_date '+ to_char(l_hire_date) )