iRule for Snat

Hi Community, i want to implement that iRule for Snat but i don't know why the f5 Big IP doesn't accept the following iRule :

Can you help me? Thanks M.

when CLIENT_ACCEPTED {
class SNAT1{
network 172.x.x.0 mask 255.255.255.0
}        

class SNAT2 {               
network 192.168.0.0 mask 255.255.255.0
network 192.168.1.0 mask 255.255.255.0
network x.x.x.x 255.255.255.0
}


    Check if the client IP address is a member of the address data group named Hosts

   if { [class match[IP::client_addr] equals SNAT1]} {

                {
                               scan [IP::client_addr] "%*d.%*d.%d.%d" a b c d
           snat 2.168.$c.$d
                }
                else {[class match[IP::client_addr] equals SNAT2]} 
                {
                               scan [IP::client_addr] "%*d.%*d.%d.%d" a b c d
           snat 3.168.$c.$d
                }   
                                                                                                                                                                                                                                           }


          Exit this event to avoid disabling SNAT below

         return


    Default action is to not SNAT

   snat none

}