Actually, even though Solomon's ability results in a card being played (the fortress) it is not actually a play ability. While that seems confusing at first, it makes sense when you think that if Iron Pan stopped that, it would also stop banding (since banding results in an additional card being played) and any other ability that results in a card being played.
Play abilities are restricted to abilities that allow you to play an enhancement, such as Hidden Treasures, Reach of Desperation, or Ethiopian Treasurer.
