Windows XP support

This may sound like an odd question, but I've been using an older version of Eraser for awhile now

From the Eraser FAQ, if you're using Windows XP, you need to use v5.6 or later for the freespace function to work(?!!)

Can anyone tell me why this is, and what the differences were between v5.3 (what I'm using atm) and v5.6 which make such a big difference?