Scantronic 9448+ Alarm Sounds on exit?

I have reset my alarm due to replacing an internal fuse - after a bit of searching for the fault!
Engineers walk test shows that all the sensors are working correctly but whenever I type the exit code the alarm goes off as soon as I close the door.
I have the zone in the hall marked as Entry/ Exit.

Any suggestions - I have the engineers code and book but I cant see where I am going wrong.