So, this happened few minutes ago on the Greedy Draft.

I had 4 lands up (2 Simic Gates, Montain, Island), Nikya of the Old Ways and a Thought Collapse. My oponnent casts Angel of Grace at the end of my turn, so he can kill me on his next turn.

I thought "great, I'll counter it, and he won't be able to kill me next turn". However, for my surprise, I wasn't able to counter his spell! First, I read the cards again to ensure I wasn't missing something, like "can't be countered" or "counter target non-creature spell", but that isn't the case.

Thought Collapse wasn't glowing to be played, so I tapped the two gates and generated 4 blue mana.... and nothing! The game just wound't let me play the spell.

In the middle of my rage and being battered by an Angel that should not exist, I ended up not taking any screenshots :(

Am I missing something? Is there any rule on Greedy Draft for counter spells I'm not aware of? Did I screw up somewhere else?