An ammonia smell could be from (as Halo suggested):

-too much nitrogen in plants (not enough flush)

Or if your weed was damp when you vaccuum sealed:

-too much moisture & not enough air
What happens in that case is the weed begins to decompose anaerobicly (without oxygen) and bacteria which develop in this environment produce byproducts with ammonia in them, like hydrogen sulfide gas - can smell of ammonia and/or sulfur (rotten eggs).

My only thoughts on how to possibly save it would be to either re-dry it and try curing again, or perhaps a water cure: Soak it first in water with some hydrogen peroxide (food grade, diluted) to kill any bacteria, then rinse it well and water cure it in plain water.

But your safest (and saddest) bet is to toss it.