Same error, I have tried deleting guerrilla camps and barracks to further lower odds, as well as changing enemy defcon with spy attacks i was able to get down to 93% but am still get the error message.
http://www.cybernations.net/nation_war_inf...ation_ID=189979 attacking regenius http://www.cybernations.net/nation_drill_d...ation_ID=122685
if it helps, my ally Daedalistan http://www.cybernations.net/nation_drill_d...Nation_ID=38760 sent a defeat alert as I was attacking(with over 95% odds at the time) he was able to attack again after deleting improvments, I was not.
edit, i am unable to further test because a second ally of mine just declared and depleted his soldiers to where i can't get worse than 99% odds)