Improved Expertise
From Neversummer 4 Wiki
Type of Feat: General
Prerequisite: Int 13, Expertise
Required for: None
Specifics: A character with this feat can make defensive attacks, gaining a +10 bonus to AC but receiving a –10 penalty to Attack Rolls.
Use: Combat
By default, NWN allows spellcasting while using Expertise; however, BioWare included a switch to disable it via scripting using the spell hook.