I'm a bit confused right now. Let's start with the cards in question.
For your combat check, bury this card to summon and play a random non-Basic weapon from the box.
If this card has the Corrupted trait, a character at your location must discard a blessing or you may not play this card.
Now, I got unlucky and Grazzle used the Wand of Sacred Weapon to summon and play the Unholy Aspergillum +3, but is alone at his location and has no blessing to do so.
According to the rulebook:
If one card tells that you cannot do something and another card tells you that you can, comply with the card that tells you that you cannot.
So, the obvious conclusion is that I can't play the weapon. However, I'm not quite sure how to proceed now, since I originally played the Wand to define my (combat) check, and that failed. The relevant rule now is this:
If a card instructs you to do something impossible, like draw a card from an empty deck, ignore that instruction.
So I'm wondering how much I am supposed to ignore. I read that as ignoring the instruction to define my check, and so I get to use another card to define it. The wand gets buried (or recharged, depending on my check), and I need to play another card to define my combat check to not end up with my Strength / Melee.
Is that correct? I could see an alternative in the aspergillum denying me playing the wand in the first place, or something strange like that.
This FAQ is relevant. I think you've played your one item on the check, but you haven't yet determined the skill. So you can play another card to determine the skill, just not another item.
Other example: Mavaro has a power that let him summon and play an attack spell for his combat check. If he summons a spell to which the bane is immune, same result.
I agree with Hawkmoon as well. You're limited to only 1 card or power which determines the skill you are using, but the wand in this case did not determine that since it fizzled. As such, you can still play another card or power to determine which skill you're using.
Thanks everyone, that's how I played it as well.