The armor was cursed before you had enchanted it. A cursed item cannot be unequipped and will often have a negative enchantment value on it.
Enchanting cursed armor or weapons will remove any curse on it.
I'm not too sure as to the cause of the delay you experienced. As far as I know, any curse is removed immediately upon enchanting the item. (Perhaps the item got cursed again, and the curse was removed by an effect such as negation? This wouldn't explain the reduced strength requirement as negation resets enchantments, so you might have run into a bug.)