Arelith

Working with a loremaster build I find I can summon three undead with my Secret Knowledge of necromancy at character lvl 9, but when I try to use my Secret Knowledge of Illusion skill at the same level it says I must be lvl 21? Why is this so?

Because sending speedy from illusion focus (or through this feat) is from lvl 21, same as -yoink and -create_teleport, etc. Summoning undead is at any point in the game.