Why won't Haunter eat the Carbos?

Question

That speed raising item, Carbos. It says "it won't have any effect" when I try to feed it to haunter. As you see below, I haven't given it max EV's yet. Why won't it eat it?

Notes (idk if they have anything to do with this)
1: Haunter is a female
2: Haunter has eaten 3 calciums before (the special attack raising stuff)

Answer 1

The EV increasing vitamins can only be used for the first 100 EVs of every stat. As you probably already have more than 100 Speed EVs, Carbos cannot be used anymore.
Source: http://pokemondb.net/ev

Answer 2

In Generation III and beyond, stats were calculated with the system of
effort values, and so instead vitamins give a Pokémon 10 EV points to
a stat, only working if the EVs of the stat raised are less than 100,
and if the total EVs are less than 510.

In other words, if you have 100 or more EVs in the corresponding stat (in this case, speed), then the vitamin won't work.

Source: http://bulbapedia.bulbagarden.net/wiki/Vitamin