Problem adding subnet to external network

Issue

• When adding an additional subnet to an ext-net that already has 5 subnets. Basically a: neutron subnet-create --name ext-subnet-5 --allocation-pool start=x.x.x.2,end=x.x.x.254 --disable-dhcp --gateway x.x.x.1 --dns-nameserver 8.8.8.8 ext-net x.x.x.0/24
  -Receive the error message:

{"NeutronError": {"message": "No more IP addresses available on network aabbccdd-1234-1234-1234-aabbccbdd123.", "type": "IpAddressGenerationFailure", "detail": ""}}