Well, you are not the first one who misclicked that dialogue option, sent 0 troops, attacked the party and ended up getting error messages.
To fix this, do the following:
1) In simple_triggers, find the trigger that starts with 1.000000 20.
2) Increase 20 by 1.
3) Insert 2133 2 144115188075857214 0 right after 21 (followed by a gap).
4) Start the game.
5) Wait till the "send troops" dialogue option is working again and error messages have stopped popping up.
6) Close the game.
7) Reverse the changes that you did to the trigger.
Keep playing as usual.