Originally Posted by Dekkah
For Elven Accuracy, you can use it ONCE during the whole MAIN Skill challenge. So you can use it (I doubt it with you second roll), but once you do, you cannot use it in an other battle untill you guys decide to end (or fail) this skill challenge. Note that if I decide to run a full battle for some reason, you will be able to use it as usual during that battle.
I'm guessing the same ruling would apply to the Human EP, Heroic Effort, which does a similar sort of thing (add 4 to an attack or save you just failed, once per encounter).