LTM Maintenance Page - error

the irule looks okay to me.

[root@ve10:Active] config  b virtual bar80 list
virtual bar80 {
   destination 172.28.19.252:80
   ip protocol 6
   rules myrule
   profiles {
      http {}
      tcp {}
   }
}
[root@ve10:Active] config  b rule myrule list
rule myrule {
   when HTTP_REQUEST {
  HTTP::respond 200 content {This website is currently under scheduled maintenance until 8AM CST on 1/19/2013!}
}
}

[root@ve10:Active] config  curl -i http://172.28.19.252
HTTP/1.0 200 OK
Server: BigIP
Connection: Keep-Alive
Content-Length: 81

This website is currently under scheduled maintenance until 8AM CST on 1/19/2013!
[root@ve10:Active] config 

have you run tcpdump to see what is going on?

tcpdump -nni 0.0:nnn -s0 -w /var/tmp/output.pcap host x.x.x.x and host y.y.y.y

x.x.x.x is client ip address

y.y.y.y is virtual server ip address