From "The Epoxy Book" by System Three Resins: Haziness and crystallization will occur if stored at cold temperatures (below 50 F.) for prolonged periods. Immersing the closed container in hot tap water and heating to 120 F. or above will bring the resin back to a clear state. NEITHER CRYSTALLIZATION NOR HEATING WILL ADVERSELY AFFECT THE PRODUCT. (Emphasis mine) Other manufacturers say the same, because it's true.

Toss it if you feel you must, but it's a waste of good material.