SNAT automap rule errors

We recently upgraded to 11.2.1 and just noticed we are getting an error for an irule that we were using and not have not really seen this error before...

iRULE :

when CLIENT_ACCEPTED {
 Check if the client IP address is a node in the VIP's default pool and active
if {[matchclass [IP::client_addr] equals [active_nodes -list [LB::server pool]]]}{

       log local0. "SNAT'ing for [IP::client_addr], member of pool [LB::server pool]"
     snat automap
 }
}

ERROR :

TCL error: /Common/ir_SNAT_Real_To_VIP - invalid matchclass operands - no class or list type found, lhs: ip, rhs: (line 2) invoked from within "matchclass [IP::client_addr] equals [active_nodes -list [LB::server pool]]"

Any ideas why, code upgrade or am I missing something in the iRule.

Many thanks J