Wall of Fire is not a creature it is a conjuration and it makes no attacks.Special: A creature can attack one
square of the wall.
Ok, people you are overlooking some thing very important. Wall Of Fire and Wall of Ice are both conjurations. Conjurations can not be attacked or damaged in any way unless the power in question says so or unless a power specifically targets conjurations.
Wall of Fire is not a creature it is a conjuration and it makes no attacks.
Given the above, a Wall of Fire can not damage a Wall of Ice.
Edit: Change last sentence after reading Wall of Ice errata.
Ah, but the -creator- of a Wall of Fire IS a creature.
That's the part that lets the Wall of Fire affect the Wall of Ice, should the creator choose to do so.
Even so, the Wall of Fire doesn't make attacks.
It does automatic damage. Since there is no attack roll involved the Wall of Ice takes no damage.
puddles don't do damage, walls of steam do!

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.