Vladesch
Warlord

I am trying to attack the orange bird head unit with my archer 2 squares to its right.
I'm currently at war with russia. When I select my archer and hover the mouse over the orange unit it shows me the combat odds and I get the red target dot (as is shown in the screenshot), but it just doesnt attack.
I can attack fine with my spearman one square to its right.
I dont get it. This has messed me up in other games before too.
Anyone care to explain to me what the problem is?