How to avoid "Access policy evaluation is already in progress"

Thanks for the link. I have downloaded the guide, but have a question about implementing the iRule in the guide. I currently have a "when HTTP_REQUEST {..." iRule that checks inbound traffic and redirects to one of two servers based on URI value. I know this is basic since I am new, but do I add a NEW iRule, or just modify the logic of my existing iRule and add this one in to it??? Also, if adding it to my existing iRule, would it matter if it is at the top or should it go in its own loop of some sort.

For discussion purposes, let me simplify my iRule and add the iRule from the manual to see if this makes sense (not sure why formatting isn't working but code starts now:

when HTTP_REQUEST { if { [HTTP::cookie exists "IsClientAppCacheEnabled"] } { HTTP::cookie "IsClientAppCacheEnabled" False }

switch -glob [string tolower [HTTP::uri]] {
"/login/*" {
    pool private_https_pool
    HTTP::header insert CERT_SUBJECT "[ACCESS::session data get session.ssl.cert.subject]"
}
default {
    ACCESS::disable
    pool public_https_pool
}

}