is the attribute Interim/Date a string attribute? If it is a date attribute, you don’t need the parseDateTime function.
if it is a string attribute, you may want to change your if statement to:
if $interim/date = empty or $interim/date = ''
then
empty
else
parseDateTime($interim/date, 'yyyy-MM-dd HH:mm')
Note that an empty string ( ‘’ ) is different than having no value ( empty ) in the attribute.
If you still get an error, you’ll want to debug this and see what the value of $interim/date is. My guess would be that there is a mismatch between the pattern you are providing to parseDateTime and the value in $interim/date.