Each room is locked to a single trinket effect, meaning that even if Isaac exits and re-enters a room, that room will always have the same trinket effect.
In rooms where the Tick effect is given, Isaac is unable to swap Error with another trinket.
If the Store Credit effect is given in a Shop, all items will be free and Error will not be consumed.
If the Monkey Paw effect is given, the fingers will not count down and you will continue to get Black Hearts indefinitely.
If the Walnut effect is given, the trinket will not be consumed and will continue to spawn items upon taking damage.
Touching a Stoney and Movable TNT counts as taking damage and will spawn a lot of items.
Error can not give the effects of trinkets you're currently holding (with Mom's Purse or Belly Button) or ones that were gulped.
Therefore, somehow gulping all the trinkets in one run will make this trinket useless.