I have a savegame from just before the attack. I couldn't reproduce the crash though.
I attacked the city Hope with the army just east of it. Started with Guardian Wind and Iron skin to defend against the arrows. Then added stone skin to the first unit that was attacked by the enemy archers.

This meant that I dodged most arrows so the battle lasted quite a long time, since my units weren't strong enough to put a dent in their armour... Maybe that had an influence?

http://mjtdevries.nl/FE/003/FallenEnchantress0_914-2012-05-13T14-57-41-687.zip

Tried the attack again with the difference that I had given my Sov Fireball spell. but this time it didn't crash. The battle didn't last as long though since with fireball his armoured units were easily (too easily) wiped away) I'll try the battle again without the fireball, to see if I can make it crash again. If I succeed I will add to this post.

But one turn later it crashed while in trade negotiations with Yithril.
http://mjtdevries.nl/FE/003/FallenEnchantress0_914-2012-05-13T15-21-23-451.zip

So far FE has been quite stable for me, (rarely crashes) so I am suprised that it has crashed twice today.

I the debug.err I see many of the following warnings: (also noticed that with the bug I reported earlier):

Debug Message:  WARNING: MemBuffer::GetString is allocating a string size larger than 1024 characters.  Requested size: 1071   If this is happening while the game is loaded, you may need a new datazip.exe file.

http://mjtdevries.nl/FE/003/debug.err

Can this have anything to do with the unstability I suddenly see?