I don't even think its the number of units that is the problem, I think problems start when we both try to move units into the same square at the same time, eg I want to add reinforcements while my enemy tries to attack... After a couple mobes we get out of sync errors...
It would be a shame if we could not finish this game, we have been playing for months (in game time = 23 hours), but deleteing troops is no option I need them all, and I am sure my opponent feel the same way.