Improved Anvil is the absolute best mod I've played, by far.
version 4.2 was just conceptually imcompatible to most other mods, because other mods add XP and items which reduce IA's challenge rate. But now version 5.0 and up will replace some of the original spells, like Mislead, with new stuff. This makes it even more incompatible, as who knows what enemy mages will cast when they were coded to cast Mislead. IA is only recommended if you're up for a challenge, and are willing to forego megamodding.
Check IA's forum here:
http://forums.blackwyrmlair.net/index.php?showforum=99
BTW Shadows over Soubar is buggy, you'll need the walkthrough at hand to avoid big errors.