Problem with resz'ing my horseman

[lobo76]

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