What happens when a bound spell is miscast depends on the nature of the bound spell.
If the bound spell is contained within a magic item of some kind, the item crumbles to dust and cannot be used again during the game. Do not roll on the Miscast table.
If the bound spell is an 'innate' ability – such as those used by a Warrior Priest, for example, then the model simply cannot cast further bound spells during this phase. Do not roll on the Miscast table.