First off as this is my first post, Zeroshell is exactly what I was looking for and works far far better than the DLink wireless router I had.
The serial needs to be updated after each update to your zone.
Initially I had a serial of 2012040900. After my first update to the zone I had to manually alter the serial, to 2012040901 but after that the serial updates automagically.
I hope this could be of help.