Mystic Armor says the critter gets it against all astral attacks. Does this include spells?

...I believe not. I think it only applies to Astral Melee.

So is Magical Gaurd the only power to give critters added protection against spells?

Unless they're sentient and magically active and have counterspelling. (such as dragons, some nagas, etc.)

There are the immunities not being sentient comes with. Depends on the spells you have in mind.

The term "Mystic Armor" is used in two places, both an adept ability and one sentence in a spell. Although not terribly clear in the text, its been made clear since that its not a spell "barrier".

A question thats come up many times in play, is can we make a spell that does create a spell barrier armor. Could with existing rules a magical guard spell be made?

My question to players is does'nt this work both ways. Would'nt it hamper spells cast by the protected party? And certainly effect spells cast on the protected party.

However, you could cast in on your non-spell-slinging friend (if Touch and not caster-only) and let him go to town. If you're one of those Possession-trad guys, you can also whip it up when you want to just rely on physical ass-kicking.

What about phys ad powers....killing hands?

But fortune, you can throw up a mana barrier around yourself for some quick extra spell protection, and cast through that just fine.

If that's really what it's trying to say, then the phrase "Mana barriers do not affect their creators," is poorly chosen.
Personally, I think the whole thing works better the way you're arguing, and I'd like to think that's what the book means, I'm just not convinced that's what the book says.

Since a spell cast by a mage is a separate magical entity from its caster, there is no contradiction between "does not affect their creators" and "any target of a spell... receives a bonus...". The caster herself is not affected. Any spell cast through the barrier is.

Following the original thought. Mystic armor does not provide protection against spells. Ok, so that leaves Magical Gaurd as the only critter power to provide extra protection against mad spell slinging players. So then can one individual have more than one source of magical gaurd working on him? Say a insect queen has three soldier spirits in attendence when runners come calling can all three soldiers protect the queen with this power? Will it stack?

It just says that the magician can see through and pass through a mana barrier, and can permit others (no specification) to do so also. Thusly, a spell is an entity which might need to pass through the barrier, why shouldn't the magician be able to permit it?

Because a spell is not considered an entity in SR4.

If a caster's spells were unaffected by a mana barrier, then specific mention would have been made to reflect that exception in the section where it states 'Should a magician try to cast a spell through a barrier, the target of the spell adds the Force of the barrier to its resistance dice pool'.

If a spell isn't an entity, then isn't the caster not being affected by the barrier the best way to say that the caster's spells aren't either? Since the spells aren't separate, then if the caster isn't affected, neither should his spells.

I still disagree that spells aren't an entity. The Passing Through Barriers section just below wards states quite specifically that spells, foci, spirits, or characters can be forced into having to pass through a barrier. So, if a spell can be forced through a barrier, then why can't a magician permit his to go through his barrier with no penalty.