Not an errata, but those templates came after the Core Rulebook and Bestiary were released. On Bestiary 2 to be exact (pages 292 and 293), which stated that they could be used on summons, but did not say how they could be summoned with the templates.
Entropic Creature (CR +0 or +1)
Creatures with the entropic template live in planes where chaos is paramount. They can be summoned using spells such as summon monster and planar ally. An entropic creature’s CR increases by +1 only if the base creature has 5 or more HD. An entropic creature’s quick and rebuild rules are the same.
Cool, so we can summon monsters with those templates, but how exactly do they work? No rules were given on the Bestiary 2, and we still had no rules saying how they worked by then.
Do we apply entropic if we are chaotic, and resolute if we are lawful? What happens if we are lawful good, does the creature obtain both resolute and celestial templates?
Later, on the Monster Summoner Handbook, we got a further expansion on those templates, with some archetypes allowing you to summon only entropic or resolute templates and feats that allow you to apply different templates to the creature summoned.
And added a bunch of new templates based on elements, such as aerial, aqueous, chthonic, dark, fiery, and primordial templates.
Considering that the archetypes restrict your summoning and the templates available and add more options, but does not allow a caster with no archetype to summon creatures with those templates.
Herald Caller Archetype
The Herald Caller (Cleric) archetype from the Monster Summoner Handbook is important because he has abilities that affect summoned monster's templates.
Divine Heralds (Su)
A herald caller can use summon monster spells only to summon creatures particularly appropriate to her deity. This includes all creatures listed as summon monster options for priests of her deity (see Expanded Summoning for Clerics), creatures whose alignment matches at least one aspect of her deity's alignment, and creatures of an elemental subtype that matches a domain granted by the deity (if any). When summoning a creature that is normally summoned with the celestial or fiendish template, a herald caller of a chaotic deity can instead summon it with the entropic template, and a herald caller of a lawful deity can instead summon it with the resolute template.
Meaning that those templates could not be normally applied to summoned creatures. And this also doesn't contradict the previous text from Bestiary 2.
But it allows the caster to be of a neutral alignment, follows an aligned deity, and still be able to summon an entropic or resolute creature. Example: A neutral good follower of Saerenrae (lawful good) would be allowed to summon resolute creatures.
Asking James Jacobs (Paizo's Creative Director) myself, I got this answer on this subject:
As written, no; those spells only allow for the summoning of celestial or fiendish creatures. Obviously, that's because the entropic and resolute templates were invented a few years AFTER we published the Core Rulebook.
Allowing for these two templates to work with summoned creatures is a great house rule if you don't want to use feats or the like.
And no, you can't apply more than one template to a summoned creature.
So, from his point of view, it's not unreasonable to allow those templates to be applied as a house rule, but since the books came on different times, they simply couldn't replace what was written on the core rulebook to allow you to summon creatures with the entropic or resolute templates.