True-Client-IP error generated. /var/log/ltm

Hmmm....not so sure on that theory - have you found anything? Maybe some of the requests are not properly formed HTTP requests and that is why it is failing. Why don't you try;

rule trueclient_ip_rule { when HTTP_REQUEST { if {[catch {HTTP::header insert True-Client-IP "[getfield [IP::client_addr] % 1]"}]} { log local0. "Caught [HTTP::request]" } } }

Of course it will probably still barf when you try to do the logging but may tell you something.