Was trying to make a barbarian/mage with SK but it seems when I start a barb, then convert to fighter w/a kit that can switch to mage, then lvl the mage and put kit back to barb (but have mage higher level than barb was) the PC can be backstabbed. What am I doing wrong?

you need to start with a fighter/mage, then you make the kit to a barbarian with sk and change both levels to 0 and then you go into the game and level up

@Gastong:
I think he's looking for a dual, not a multi.

@TT:
I don't know what you're doing wrong, but that's because I don't know exactly what it was you were doing. It would help if you went step-by-step through what you did so we can better see any potential mistakes.

I just looked through my clabfi05.2da, and it never states that the barbarian is immune to backstab, it has movement speed at level 1, the rages at the various levels it gets it, the damage resistance at level 11, 15 and 19 but it never says that hes immune to backstab

You could use the G3 Tweak Pack, which makes the dualclass possible without resorting to SK. http://www.gibberlings3.net/g3tweak/index.php