Alliance Woes

I'm having some trouble offering/joining an alliance with a computer player during a standard game.

I encountered the computer, and sent him a message proposing a new alliance. I enter the appropriate restrictions for the Alliance, choose a name and an icon, and send the message.

The next turn, he invariably responds to me with a message that says "we propose a new alliance". When I look at the options of the alliance, they are identical to mine, but I have no option to accept or decline. All I can do is click "view" to look at the alliance settings.

How can I actually enter into an alliance with this computer player?

I currently have no treaties and the computer player in question is "receptive" to me.