It could be a conflict. With on text events, if you have three events and the first one catches something, mIRC stops looking for more events that will match in that document. example:

Code:
on *:TEXT:*hello*:#: { ... }
on *:TEXT:*be right back*:#: { ... }
on *:TEXT:*goodbye*:#: { ... }


Now, if a user says "hello everyone, I'll be right back" the first event will trigger, but the second will not. Why? Because mIRC has found a match already and does not continue further. To solve this, try using if statements:

Code:
on 1:TEXT:*:#: {
  if (*register nick* iswm $1-) {
    bt $chan 3 To Register you nick first you choose a nick by typing /nick Worzel then you register that nick by typing /nickserv register *a password of your choice* *your email* 
    bt $chan 3 But you must not enter the * symbols, for example you would type /nickserv register 123456 worzel@gummidge.com
    bt $chan 3 Then to identify yourself you type /nickserv identify 123456
    bt $chan 3 123456 being YOUR password.
  }
  if (*welcome to the room* iswm $1-) {
    bt $chan 3Please register on the $chan 's web site for latest news and bloggs and forums and help and advice. The address is 4http://www.simonsforums.org 3It is free to register, all we ask is you use it regular and spread the word to allow the room to grow from strength to strength. :)  Thank You.
  }
}

on 3:TEXT:*:#: {
  if ([color=red]*be right back*[/color] iswm $1-) {
    if ($nick isop $chan) { bt $nick 3Please ensure that if you are going Away From Keyboard to downgrade yourself from Op Status and Op up another Op.  If you already have your status as a none Op there is nothing to do. :) }
  }
}


Hope that assists you in some way.