Code:
on *:start:{
  server irc.efnet.nl
  server -m stockholm.se.eu.undernet.org
  server -m irc.freenode.net
}
on *:connect:{
  if ($network == EFnet) {
  join #bla,#blo }
  if ($network == Undernet) {
  join #bla,#blo }
  if ($network == freenode) {
  join #bla,#blo }
}


Make a new remote file from the script editor, by going to File > New put the above code in that, and change #bla,#blo as necessary. If it's in a completely new file it should work, the reason it's not connecting is probably because it's conflicting with something else.

Perform would not affect the ON START event as Perform does its commands once you have connected. To make sure nothing interfers with the ON CONNECT event however, type /perform off.

Regards,