When I cast this I am getting a "failed" message.

Is anyone else getting this? I know it has a 15 minute recast but even after several hours it still isn't resetting.

it on the same buff line as the cleric mit buff.  meaning if you have a merc out you probly wont be able to use this unless it a long fight

how good is the effect though? noticeable difference in dmg taken?  or is it one of the ones ill get later on down the line...

The main benefit is that it can mitigate a total damage that is, when maxed aa level, 18,000 hp total vs say your merc's Vie line which is like 4400 hp or so.  However it gets replaced by your merc healer Vie line, since the cleric's Vie line is 10% mitigation whereas this is only 5% (up to a total of 18,000 as stated above).
When I LOD burn I never have my healer merc up... obviously.  So I make sure I have his line of Vie beforehand... then as it dissipates from me taking hits, I then cast our protection of the warder aa, since I am going full out and don't want to stop and bring merc up etc.  It lasts for a long time however due to it been able to mitigate a total amount that is way higher than any other mitigation buff.

At the end of the day 5% ain't a whole big number but it's yet another aa that is beneficial for sure in the "every bit helps" department.

aye but its small compared to say

Protection of the Spirit Wolf    
 
Slot    Description
2:    Mitigate Melee Damage by 35%, 20000 total
3:    Mitigate Spell Damage by 35%, 20000 total
4:    Increase Magic Resist by 120

or even

Outrider's Evasion    
 
Slot    Description
3:    Decrease Accuracy by 150%
4:    Increase Chance to Avoid Melee by 75%
8:    Increase Movement by 100%
9:    Mitigate Melee Damage by 10%

Both of these are ranger AA the second one has no damage amount even

WILL NOT stack with cleric Via,



 5% OF HI'S TO 18,000 hP. LASTS 7 MIN RECAST 15min

  i find it works nicely to tell ya the truth i like it.