Melee Units Unable to Attack Friend's Units

I'm playing with four friends, I am playing as Zulu and I have just declared war on one of my friends who is playing as Egypt.

We turned simultaneous turns on because not having it on cause problems in an earlier game such as no one being able to do their turn. Even though it is off, we have a system were we take it in turns to do our stuff. I had my vast armies readied up about to reveal itself to my friend but when they do and I was about to attack his lancer, it didn't work.

It shows the swords icon and when click the cursor turns red and the red circles appear around the units I can attack but when I click on his units it simply doesn't do anything. The unit can still do stuff but every time I try and attack it does that.

At first I thought it was because of my Impi but I tried it with my musket men and it ended with the same effect. I can bombard his units with cannons but nothing else will work.

I will try again tomorrow and see if saving the game where we were and starting it up again works. I'll post if it does or doesn't.

Any help would be appreciated!