Fairy Tail Thread (Spoilers)

If Gray could spam his magic, why couldn't Rufu spam his anti-magic magic? xD

Because. Each Sword/Weapon was made differently. Rufus "Memorize- forgotten" magic requires him first to at memorise the magic being used, which takes a short time, then to manually cancel it with his "forget" spell. Initially he WAS going to memorise the spell grey was using, and then cancel it (You can see him start to do it, page 17 on mangastreams version).

But then Grey started casting tens or maybe even hundreds of different Ice Make spells in quick succession, and , like Rufus said, he couldn't memorise that many spells that quickly, so he could not cancel them.