Persitence via Xfor

Hello, I have a problem with the balancing of some systems. In the diagram below you can see the current balancer configuration.

Internet --> FrontEndF5 --> SecureProxy --> BackEndF5 --> Ohs-Pool --> BackEndF5 --> PortalServer-Pool

What I would like to achieve is to be able to balance the servers in the Ohs-Pool and the servers in the PortalServer-Pool using the Xfor field. From the logs I can see that the HTTP::header field "X-Forwarded-For is valid, but the iRule I created seems not to work and I get an error from the web portal.

My iRule:

when HTTP_RESPONSE {
if { [HTTP::header "X-Forwarded-For"] } {
persist add uie [HTTP::header "X-Forwarded-For"]
}
}
when HTTP_REQUEST {
if { [HTTP::header "X-Forwarded-For"] } {
persist uie [HTTP::header "X-Forwarded-For"]
}
}