After a few tries i simply reloaded my save once more and left the mission behind. Next i attempted one of the early main quest missions. Same thing happened at a certain point during that mission, and so i reloaded, rinsed, repeated, problem persisted. Just to be sure, after i reloaded my previous save i did a minor side quest and found that i was still able to duplicate enchanted armor afterwards. Why i was able to do that and not the other more important missions is bizzare.
Has anyone ever noticed this? It seems to only prevent me from duping armor pieces. Enchanted Rings, soul gems, scrolls, etc, are still elegible to be duplicated. I'm using the scroll method of duping, also i'm running a sizeable amount of permanent enchantments on my character (40-50 separate items). It seems like i reach some random point during a quest and i can no longer duplicate armor. I know i can still permanently enchant using rings and amulets, but its still pretty annoying.