404 status issue

A page is merely a collection of objects for which HTTP GET requests must be made. If for instance a page had 12 images, a 404 for any of them could trigger the rule. Also, HTTP::host shouldn't be used in HTTP_RESPONSE since there's no host header. You'll want to set a variable from HTTP_REQUEST and check the variable from HTTP_RESPONSE.

Something like this would work:

when HTTP_REQUEST {
  set hostvar [HTTP::host] } }

when HTTP_RESPONSE {
   if { [HTTP::status] eq "404" } {
  if a 404 is returned, send a 301 redirect for our custom 404 page
    HTTP::respond 301 Location "http://$hostvar/portal/site/erp/404/" } }

Let me know if you have any issues with that.