One of my SideKick, the Paladin Guy died. I used the Raise Dead Spell on him to no avail.

I'm in the Mine, Act1.

Other than being a pain to target sometimes I've never had a problem with raise dead. If you have the required mana (100 iirc) it should be just a matter of selecting the spell on the quickbar and right clicking on the corpse. Finding the corpse in the small confines of the mines passageways is sometimes a trick in itself.