First some good news - we are doing a major marketing move with huge increase to population growth expected with-in a week, so the problem in finding a random PvP or CoOp partner should be fixed.
Now to the OOS issue. This is an extremely rare occurrence in CoOp. I would recommend trying to attack a different town. In addition try to recreate your and your friends armies. (Choose to Split army and transfer all the units into the new army)