Collectible Card Game Headquarters

I tried to declare blockers with creatures that were summoned during my last turn and still had summoning sickness. The software would not let me declare those creatures as blockers, and I don't understand why. In addition, I tried to declare a non-monstrous creature as a blocker, but clicking on the creature, only asked whether I want to make the creature monstrous (I did not have enough mana). I could not get the creature to block.