I've had this happen on two characters now; during the build phase, a Tower that I have built recently, and that I have enough mana to build again, won't allow me to build it.
This last time it was on my Monk. I had the 30 mana to place another Ensnare Aura and yet the UI said I couldn't do it. Is there a stat I need to boost to place more than a few of the same Tower?
Best Answer
It's possible that you are out of Defense Units.
Every defense (trap, aura, tower) costs a certain amount of Defense Units to place down. You can see this when inspecting a defense, as well as in the radial menu when inspecting your hero defenses.
In the top right corner of your screen should be a number xx/yy, where xx is the current amount of defense units that you've used and yy is the total number of defenses allowed for the level that you're on. If you are out of defense units, or don't have enough for the defense you wish to place, the game will not allow you to put one down.