Ero Gaki said:Actually you can cast a scroll on the defensive. If you look under the "Activate Magic Item" section in the Combat chapter, it stats : "Activating a spell completion item, such as a scroll, is the equivalent of casting a spell. It requires concentration and provokes attacks of opportunity. You lose the spell if your concentration is broken, and you can attempt to activate the item while on the defensive, as with casting a spell."
Just goes to show you: Keep a thread alive long enough and SOMEONE is bound to find the right answer.