iRule error message

Hello,

my iRule keeps producing the following error message:

TCL error: clean_incoming_xff  - Operation not supported (line 1)     invoked from within "HTTP::header remove "X-Forwarded-For""

the iRule itself:

clean_incoming_xff:
when HTTP_REQUEST
{
    HTTP::header remove "X-Forwarded-For"
    HTTP::header remove "X-Forwarded-For-Extended"
    HTTP::header insert "X-Forwarded-For" [IP::client_addr]
    HTTP::header insert "X-Forwarded-For-Extended" [IP::client_addr]:[TCP::client_port]
}

Is there an error in the iRule?

Thanks in advance for any hint.

Milan