problem with ippool module

[Rubenb]

Im using freeradius 3.2.4 , I have a problem that I couldn't set up 
ippool module. When I do a symbolic link with mods-enabled and 
mods-available of ippool module , I set up ippool module with two pools.

Then when I go to start the service freeradius with systemd , it couldnt 
start , syslog says:

/"rlm_ippool: Failed to open file /etc/freeradius/db-users.ippool: 
Read-only file system"
"/etc/freeradius/mods-enabled/ippool[67]: Instantiation failed for 
module "users_employee""/

this is my config of ippool module:

/ippool users_employee {
     filename = ${db_dir}/db-users.ippool
     range_start = 192.168.248.1
     range_stop = 192.168.248.254
     netmask = 255.255.254.0
     cache_size = 800
     ip_index = ${db_dir}/db-users.ipindex
     override = no
     maximum_timeout = 0
}

ippool it {
     filename = ${db_dir}/db-it.ippool
     range_start = 192.168.249.1
     range_stop = 192.168.249.254
     netmask = 255.255.254.0
     cache_size = 800
     ip_index = ${db_dir}/db-it.ipindex
     override = no
     maximum_timeout = 0
}/

The config example in the file ipool module says that I can put the same 
config that the file ipool module in the radiusd.conf base config file , 
but its the same because radiusd.conf have an include of mods-enabled so 
the config that I have in ipool module is supposed that its going to be 
charged by the service.
If I do "freeradius -X" , the service start in debugg mode with 0 
problems , and I can see that freeradius in debugg mode charged the 
module ippool.

I want to use ippool and not sqlipool , I have this: opnsense (openvpn 
server instance) + freeradius (ldap + ippool) + openldap.

I have openvpn server instance in opnsense working and openldap with 
freeradius ldap module working. Now I need to implement ippool module to 
create two pools for two groups of LDAP.


I need to know if I am missing something important with ippool module , 
thanks in advantage.

--