LAST EDITED ON Apr-19-05 AT 10:37 PM (Pacific)I too have experienced this bug while playing the PC version. Just the spells you have waited forever for, the ones that make your spellcasters useful at the end of the game (Nuclear Blast, Death Wish, Word of Death, Asphyxiation, Mind Flay) become 100% ineffective, and you're forced to attack enemy groups one at a time with Fireball, Iceball, etc. Every now and then, your spells will blast away and kill all of the enemies, but then in the next battle-- even against the exact same type of monsters-- your spells won't do a single thing.
I did read something on a Japanese website that may explain the bug in certain versions of Bane though. According to this website, the effect-all-monsters spells become 100% ineffective (regardless of your level, the enemy's level and resistance) when the first enemy group has been partially or completely diminished. From my understanding, the website goes on to suggest having your fighters not attack the first enemy group while your magic users use their mass-target spells, and if the first enemy group is especially dangerous, put them to sleep or paralyze them, as long as you keep them alive the longest.
I will test out this theory the next time I play Bane!!!
If you understand Japanese and want to check it out for yourself, this website (about Bane mainly) is awesome and explains some of the differences between the different versions of BCF, such as Super Famicom or PC.
http://www8.plala.or.jp/Wizardry/chisiki.html