GabiMoro: Elixir of life is an artifact set. He is made from these artifacts:
Ring of Life
Ring of Vitality
Vial of Lifeblood.
That means Elixir of life requires 3 empty slots on your Hero inventory: 2 ring slots and 1 misc, slot.. Strip your hero from his 2 rings (if he has any) and 1 misc. artifact and you could equip Elixir of Life.
iLiVeInAbOx: Erm, thank you for responding but either you didn't understand what I wrote or you didn't actually read my post :) The problem is that the artifacts I can get by trading the seers for the elixir do not equip. Ie. I give them the elixir and they give me something else. The something else's do not equip.
Sorry, I wrongly understood that you can not equip Elixir of Life. I think the Seer huts give you these artifacts in exchange for Elixir of Life: the Wizard’s Well, the Ring of the Magi, the Bow of the Sharpshooter, or the Power of the Dragon Father.
All of these are Artifact Sets which requires more empty slots on you hero inventory.
For ex. the Wizard’s Well is made from:
Charm of Mana
Talisman of Mana
Mystic Orb of Mana
All these artifacts are Miscellaneous artifacts so you hero must have 3 empy misc. slots. (3 empty nr.9 slots on this image:
http://heroes.thelazy.net/wiki/Artifacts).
The easiest way to find out which slots do the artifact need is to unequip all hero's artifacts until the new artifact can be equiped.