Unexplained TCL Error on iRule

I have taken over a system with an iRule producing following error. The thing is running on a sensible production environment and seems to do what it should... but the error is polluting my logs.

Error: 

Mar 2 13:13:55 slot1/waf err tmm1[21022]: 01220001:3: TCL error: /Common/RewriteUrl - Operation not supported (line 10) invoked from within "HTTP::header replace "Host" intranetprivate.site.cl.eu" ("10.10.." arm line 4) invoked from within "switch -glob [IP::client_addr] { "10.10.24.15" { log local0. "CLIENT: [IP::client_addr]:[TCP::client_port] -> [HTTP::host][HTTP::uri]" ..."

iRule:

when HTTP_REQUEST {
    set DEBUG 0
    if { $DEBUG } {
        set LogString "-Before- Client [IP::client_addr]:[TCP::client_port] -> [HTTP::host][HTTP::uri]" 
        log local0. "============================================="
        log local0. "$LogString (request)"
        foreach aHeader [HTTP::header names] {  
            log local0. "$aHeader: [HTTP::header value $aHeader]" 
        }
        log local0. "=============================================" 
    }
    switch -glob [IP::client_addr] {
        "10.10.24.15" {
            log local0. "CLIENT: [IP::client_addr]:[TCP::client_port] -> [HTTP::host][HTTP::uri]" 
            HTTP::header replace "Host" intranetprivate.site.cl.eu
            HTTP::header replace "host" intranetprivate.site.cl.eu
        }
        "10.10.24.249" {
            log local0. "CLIENT:  [IP::client_addr]:[TCP::client_port] -> [HTTP::host][HTTP::uri]" 
            HTTP::header replace "Host" intranetprivate.site.cl.eu
            HTTP::header replace "host" intranetprivate.site.cl.eu
        }
        "10.10.*.*" {
            log local0. "CLIENT: [IP::client_addr]:[TCP::client_port] -> [HTTP::host][HTTP::uri]" 
            HTTP::header replace "Host" intranetprivate.site.cl.eu
            HTTP::header replace "host" intranetprivate.site.cl.eu
        }
        default {
            HTTP::header replace "host" intranetprivate.site.cl.eu
        }
    }
    if { $DEBUG } {
        set LogString "-After- Client [IP::client_addr]:[TCP::client_port] -> [HTTP::host][HTTP::uri]" 
        log local0. "============================================="
        log local0. "$LogString (request)"
        foreach aHeader [HTTP::header names] {  
            log local0. "$aHeader: [HTTP::header value $aHeader]" 
        }
        log local0. "=============================================" 
    }
}
when HTTP_RESPONSE {
    if { $DEBUG } {
        set LogString "-Before- Client [IP::client_addr]:[TCP::client_port]" 
        log local0. "============================================="
        log local0. "$LogString (response)"
        log local0. "status [HTTP::status]"
        foreach aHeader [HTTP::header names] {
            log local0. "$aHeader: [HTTP::header value $aHeader]"
        }
        log local0. "=============================================" 
    }
    switch -glob [IP::client_addr] {
        "10.10.24.15" {
        }
        "10.10.24.249" {
        }
        default {
            switch -glob [HTTP::status] {
                "30*" {
                    HTTP::header replace "Host" intranet.site.cl.eu
                    HTTP::header replace Location [string map -nocase {intranetprivate.site.cl.eu intranet.site.cl.eu} [HTTP::header value Location]] 
                }
            }
        }
    }
    if { $DEBUG } {
        set LogString "-After- Client [IP::client_addr]:[TCP::client_port]" 
        log local0. "============================================="
        log local0. "$LogString (response)"
        log local0. "status [HTTP::status]"
        foreach aHeader [HTTP::header names] {
            log local0. "$aHeader: [HTTP::header value $aHeader]"
        }
        log local0. "=============================================" 
    }
}

Cheers St.