From the Helpfile:
The -m switch creates a new server window for that connection and connects to the server. The -n switch does the same thing but does not connect to the server.

So the code of the above example should look like this (note the missing -m in the first server line):
Code:
  
on 1:START:{ 
  server irc.criten.net:6667
  server -m irc.sandnet.net:6660
}

DALnet: #HelpDesk, #mIRC, #MISHScript - Undernet: #mIRC, #mIRC-Scripts