mIRC supports auto voice and auto op already. Besides, this code is very hard to setup and could be executed much differently. You also don\'t check if you are an op in the channel. I\'m not even sure it would work looking at the code.
Here is a resolution:

1) Use a global variable (%opvoice.nicks for example)

on @*:join:#:{ 
  if ($istok(%opvoice.nicks,$nick,32)) mode # +vo $str($nick,2)
}

Then it is easier to add nick by using //set %opvoice.nicks $addtok(%opvoice.nicks,NICK,32)

Second solution:
/avoice nick
/aop nick

OR:
(Another example, doesn\'t exactly have to be done this way)
/auser opvoice nick
on opvoice:join:#: if ($me isop #) mode # +vo $str($nick,2)