IRULES - LB::reselect

I have testing this irule so i have three errors:

What is the probléme, i can't create a variable in a irule? Or its not the right method?

the error:

01070151:3: Rule [/Common/irule_TEST] error:
line 1: [command is not valid in the current scope] [set poolname "TEST"]
line 2: [command is not valid in the current scope] [set fqdn "TEST.com"]
line 3: [command is not valid in the current scope] [set NbNode 2]
line 16: [command is not valid in current event context (HTTP_RESPONSE)][LB::reselect pool $poolname]

the script:

set poolname "TEST"
set fqdn "TEST.com"
set NbNode 2

when HTTP_REQUEST {
    if { [string tolower [HTTP::host]] equals $fqdn }
    {
        pool $poolname
    }
}

when HTTP_RESPONSE {
  if { ([HTTP::status] == 500) or ([HTTP::status] == 404) or ([HTTP::status] == 503) } {
    if { [active_members $poolname] > $NbNode } {
      LB::down
      LB::reselect pool $poolname
    }
    else {
      LB::reselect pool $poolname
    }
  }
}