Will the following setup work

So i have the following setup and for some reason it worked till today and now i dont know why its not working

i have a dell r200blade with 2 NIC one going to another sip server using sip on a dedicated connection and one going to the fortigate firewall.
the NIC that is going to the fortigate firewall has 2 virtual IP’s
10.0.0.100 with a gateway of 10.0.0.1 and subnet 255.0.0.0
and another virtual ip with an external IP
212.119.XXX.XXX

i have users with ip’s 10.4.1.1 and with legal IP addresses
the users with the legal IP Address all register without a problem and now the local users dont work!
up until today they were both working i didnt change anything and boom it stopped working
my sip.conf has in it
nat=yes
externip= 212.119.XXX.XXX
localnet= 10.0.0.0/255.0.0.0

what could be wrong ???
so far i have been working on this over 14 hours! i need help!!!
i am still working on it and i will write an update if i have one!