Problem with resz'ing my horseman
 

While still in Darion, I was able to bypass the army guarding the knight's camp and hire horseman from there. Even with their 130 hitpoints, sometimes they will die. However, when I ready my resz spell (spellbook/inqusitor ability), I couldn't cast on them.

Am I too low level? But I could resz the archmages who were also level 4 units, so I don't think this is the reason. though I don't use them anymore (only 15 of them in the camp), I just curious to know why. Is it just a bug?

currently, level 7 paladin

There is one case that I know you can't perform resurrection like you normally did. It is when you increase the stack with sacrifice (at least in my version). Let's say you increase your horsemen by 1 with sacrifice and then lose it in the same battle. You will not be capable of resurrecting the lost horseman.

thanks for the answer. But i realised that it was because my spell level was too low to rez a lvl4 unit. i had inquistors before, and had no problem rez-ing them. Hence, when I got rid of them, I was wondering why they can't be rez anymore.

upgrade your spell...
Res lvl1: units lvl1-2
Res lvl2: units lvl1-3
Res lvl3: units lvl1-4

Unit level 5 can not be resurrected with a spell. (I think I read somewhere that inquisitors can resurrect them though)

Yes the Inquisitors can resurect them. Still, they have limitations too, i think they cannot resurrect some other units, like dragons.

As far as I know, Inquisitors can resurrect everything except plant, undead, Cyclops and Black Dragon.