I don't know if this helps, but all I did was click in Inv. at the top, clicked on "Edit Library", searched for the item I wanted, added it to the character's inventory, then saved that character to my "MyGames" folder where the Terraria .plr saves are located.
When I attempt to load the player, I get a character with a greyed out name that says "(UnknownError) Player".
Never had a problem with it before, and I'm not sure what the deal is. I even tried to load one item onto the character and save it. Still can't load the character after that.