iRule Error when try to disable ACCESS in HTTP_REQUEST_DATA event

Can we disable APM profile in HTTP_REQUEST_DATA event?

when HTTP_REQUEST_DATA {
    Parse XML Data
    set xmluserdata [findstr [HTTP::payload] "" 10 ""]
    set xmlpw [findstr $xmluserdata "" 10 end]
    if {!([info exists "xmlpw"])} {}
     unset xmlpwtmp
}

When I try ACCESS:: disable as follows: if {!([info exists "xmlpw"])} { ACCESS::disable} [command is not valid in current event context (HTTP_REQUEST_DATA)][ACCESS::disable]

I don't want to initiate APM module if password is empty.