Rune Chain Spell not working - after selecting friendly troop

[Harakiri]

It does not work for me - when i select my friendly troop e.g. runemages which give me +300% - i cant select an enemy drop enemy - the magic wand still shows but it doesnt highlight enemy units nor does left click do something - and as i said - it then shows the hourglass and nothing happens

this really sucks, because it would do 5000 damage for only 7 mana for me