This isn't a homework problem, but it won't let me post on the other page. A well known vector identity is that rot(rot(E)) = grad(div(E)) - div(grad(E)). I've actually used this before without encountering any problems, so I don't know if I'm just having a brain fart or something, but shouldn't grad(div(E)) be equal to a vector and div(grad(E)) be equal to a scalar? How can you add or subtract them? It doesn't make any sense.