TEXT: Chapter Approved – Codex: Eldar Q&A v2.0
  Q. Does the Wraithlord get cover saves?
  A. Yes, but the cover in question needs to be at least half the height of the
  model.
  Q. Are krak grenades or meltabombs usable on Wraithlords?
  A. No, they are only useful against vehicles and immobilized Dreadnoughts.
  Q. Does the Guide psychic power affect vehicles?
  A. Yes.
  Q. What is the cost of a Warlock on a jetbike? In the Warlock Bodyguard
  entry it says it costs +25pts for a total of 36 points, whilst in the
  Guardian Jetbike Squadron entry it gives the cost as 41 pts.
  A. 36pts is correct.
  Q. Does the Fortune psychic power affect vehicles, such as those
  designed with the VDR rules that allow some Eldar vehicles a 4+
  invulnerable save?
  A. No.
  Q. Are Exarch powers, such as Burning Fist, considered to be special
  weapons?
  A. Yes, which means they are only of benefit if in base-to-base contact with
  the enemy.
  Q. Does a Wraithlord have to strike last as it has Dreadnought close
  combat weapons? Some people are quoting page 91 of the rulebook:
  “for Dreadnoughts close combat weapons count as power fists, but it
  strikes according to its normal Initiative value instead of always striking
  last.” They are focusing on the part ‘for Dreadnoughts’, and using that
  to say non-Dreadnought units with Dreadnought close combat weapons
  strike like a power fist.
  A. Tell anyone who asks this one to stop being so bloody literal! They do not
  Q. The Warlock power, Enhance, is not cumulative. Is this correct (five
  warlocks in a retinue would not boost WS by +5)?
  A. Correct, it is not cumulative.
  Q. Can you use both the crystal targeting matrix and star in the same
  turn? It seems a way to get around the star engine firing in the Shooting
  
  phase to shoot with the crystal targeting matrix in the Movement phase.
  A. No, you shouldn't be able to fire when you use the star engines.
  Q. Under the support weapon battery it says that each Guardian is 20pts
  per model. Is this correct (D-Cannon 70pts= 40pts for two crew + 30pts
  for weapon) or is that 20pts for 2 Guardians (D-Cannon 50pts= 20pts for
  two crew + 30pts for weapon)?
  A. The points value is per gun and crew, then the type of gun is added on top
  (per model includes the weapon and two crew members. This could have
  been made a little clearer).
  Q. Do Warlocks count as an HQ choice or are they treated like a
  Command squad/Retinue and do not count as a separate choice? I only
  ask because it doesn’t say that they aren’t counted as a separate HQ
  choice like similar units in other Codexes. To us it would seem that they
  are counted as an HQ choice.
  A. They are not a separate HQ choice, so treat them like a bodyguard.
  Q. Do the Warlocks that are assigned to units other than the Farseer still
  count as HQs for the Space Marines' victory conditions in the Planet Fall
  mission?
  A. No they don't, they effectively become part of the unit, much like a Veteran
  Sergeant, and this means they're also counted for half-strength, etc.
  Q. Can you choose the model targeted by Mind War and can you use the
  power in close combat.
  A. Mind War is an ‘instead of shooting’ attack so cannot be used if the caster
  is in close combat. You may select the model to be attacked as long as you
  can draw a legitimate line of sight to it. Remember that close combats block
  line of sight and that you cannot target squad members in transports.
  Q. Another fast one on Mind War: If you have an Invulnerable save & are
  hit with it, do you make one save against all the effects (say multiple
  wounds) or a save against each wound result you take (say if you lost
  by 3, you roll against a save versus each one)?
  A. Save against each wound separately.
  Q. When a mission targets HQ leaders for its goal, who is the target in
  the Seer Council? (There is no precise leader model in that unit.)
  A. Tricky... I'd go for the Farseers, who must all be killed to qualify (tough I
  know but I don't see a more logical choice).
  Q. Warp Spiders and the Withdraw power. Are these usable when: a) an
  
  enemy unit has lost and then passed a Morale check? b) an enemy unit
  has lost and then failed a Morale check? c) the Warp Spiders unit has
  lost and then passed a Morale check? d) the Warp Spiders lost and then
  failed Morale check (and then regroups under power description)? e)
  there is a tie on Morale High Ground?
  A. According to the Codex it's used at the end of the Assault phase, so that
  would mean on a, c or e since on any other result one side or the other would
  be falling back.
  Q. Can a model use Fleet of Foot to embark? I can see where it's not
  officially' in the rules but I can't see where it could be abused, so I
  thought I'd ask you folks. We had also assumed a model could indeed
  move in his transport, get out 2”, then Fleet of Foot, then assault – any
  problem there?
  A. No, embarking or disembarking is a manoeuvre that must be done in the
  Movement phase unless specifically stated otherwise.
  Q. The Seer Council used the Fortune power throughout the game to re-
  roll their saves. We were under the impression that they could not do
  that, since the Fortune power SPECIFICALLY identifies Armour and
  Cover saves and doesn't mention Invulnerable saves (two out of three
  mentioned seems pretty intentional).
  A. Fortune does apply to Invulnerable saves. Unfortunately Gav assumed that
  the Rune Armour save, being Invulnerable, would be covered by the wording
  (Doh!).
  Q. Can a Space Marine Psychic Hood work against Warlock powers?
  And if so, how? When do you get a chance to nullify the Warlock power?
  A. Against Enhance, Embolden and Conceal, the Librarian can use his
  Psychic Hood at the start of a Space Marine turn against one Warlock. If he
  successfully nullifies the power then it has no effect for the rest of the Space
  Marine turn. Against Destructor it works as normal, except of course that there
  is no need for the Warlock to pass a Psychic test first  simply announce you
  are using the Psychic Hood when the Eldar player declares he is using
  Destructor.
  Q. When I fire Wraithcannon at a skimmer moving more than 6” can I
  score
  a penetrating hit?
  A. No, all hits are assumed to be glancing only.
  Q. Can an executioner blade count as an additional close combat
  weapon?
  A. No, it requires two hands to use so cannot be used as an additional
  
  weapon.
  Q. Where do I draw line of sight and measure range from when firing a
  support/heavy weapon platform?
  A. You need line of sight both from a crewman and the weapon, range is
  measured from the weapon. The exceptions to this are the D-Cannon and
  Shadow Weaver, which do not require line of sight.
  Q. Can A Warlock select runes of witnessing to help with powers such
  as Augment?
  A. Yes
  
SOURCE: textdata/thevault/Warhammer/40k/1st-8th Editions (Prior)/Errata/Warhammer 40k - Errata - Eldar QA.pdf