This is inconsistent but I've died 3 times from not being able to heal myself because of a "Target is Immune" message, this only seems to happen when fighting multiple Lujien, usually Feral types. Have any other healers had unexplained deaths fighting the werewolves or noticed the "Target is Immune" message while having a werewolf targeted and trying to heal yourself? Next time it happens I will have to try F1 heal and retarget. Oh and I have no merc out and definitely targeting the werewolf. The spells I remember using were Cure (with heal AA), Regrowth VIII & Hibernation. Probably the one shot heals too.
There are some debuffs that mobs can put on you that make you, temporarily, immune to benificial spells... which includes heals. Next time it happens, check what debuffs are on your toon. One of them is most likely the culprit. And, icing on the cake, cure is a benificial spell too.. so you can't cure the debuff either.
I have noticed this before also. I usually don't cure on solo fights but after noticing my low health on a fight I used group heals and that seemed to work.
