in 5.0 GA, GUI has check for zone type (single interface zone and normal zone), so when there has device zone mapping or policy pacakge used this zone, then type can not change
thus if current zone is single interface zone, you can not add more interface to this zone
in 5.0.1, we will try to remove some check and make change zone type easier for most cases
in GA, a possible workaround is to run a script on ADOM db, to force to change zone type from single to normal
config dynamic interface
edit xxx
set single-intf disable
next
end
the main difference is, single interface zone will install interface policy to FGT, and change to normal zone will install zone policy to FGT, so you may see many policy delete/re-create during install
Thanks
Simon