The server you're connecting to uses name based hosting. Use HTTP/1.1 and specify the host name in your request headers.
Code:
alias hread {
  sockopen hread www.maxoctane.net 80
}

on *:sockopen:hread:{
  sockwrite -n hread GET /humveeupdate.txt HTTP/1.1
  sockwrite -n hread Host: www.maxoctane.net
  sockwrite -n hread User-Agent: mIRC $version
  sockwrite -n hread
}

on *:sockread:hread:{
  if ($sockerr) return
  sockread 942 &temp
  echo -s -------------------------------------------------------
  echo -s Getting Update Information, Please Wait.
  echo -s -------------------------------------------------------
  echo -s  Update Information:
  echo -s $bvar(&temp,1-).text
}