Today I got to the Chamber of the Charmed with my newest character, but for some reason when I tried to attack the Soulkeeper, none of my attack cards would work. I had over 160 mana, I was using a card that was lit (in other words, I had enough pips), but the attack cards just would not give me a green checkmark indicating I could use it against him - no matter what I tried. I have seen something like this posted before and people usually reply "You didn't have enough mana" or "You didn't have enough pips" but I had plenty of both.
Luckily I had crowns so I could purchase a henchman for 20 crowns, but, if I hadn't, I wouldn't have been able to get past this quest at all.
I ran into the same problem a couple of days ago, but managed to figure out that clicking the enemy's nameplate instead of the enemy would allow the spell to be cast.
Supposedly that glitch was fixed in the last update. Apparently it wasn't fixed everywhere.