Account bound and Character bound are two different things. At least one artifact Eye of Lethandar becomes bound on pick up to the character who pulled it from the chest. Other have to be equipped to be become character bound. Once a character uses an artifact it is bound to the character forever.
For account bound items, you must enter your @Name in the address field *before* you try to attach an item. The item must also be either unbound or account-bound. Character-bound items cannot be traded with other players (including your alts). Any artifact you have used becomes character-bound.
Based on your description you are trying to attach the item from inventory before you put in your @name into the address field.
Actually, you get the 'this must be addressed to yourself' message, even if you are trying to attach a character bound item. I think it is generic. Adding a specific trap to catch which message to display would alleviate this, although it probably isn't forthcoming.
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Based on your description you are trying to attach the item from inventory before you put in your @name into the address field.