Unable to issue attack orders.

In game session 1345343, I have suddenly become unable to issue attack orders. Regardless of which unit type I select, when I try to issue an attack order I get the error: "The server state does not match the client"

Everything else works normally. I have tried; restarting my browser(s), logging off and back on, clearing my cache, different browsers, and different PCs altogether. I am not having the problem in any other session.