Seems to be a buggy with goto loops, with while loops it works fine.

Code:
dialog adc {
  title "New Project"
  size -1 -1 140 45
  option dbu
  button "Button", 1, 20 11 37 12
}

on *:dialog:adc:sclick:1:{
  /*
  set %test1 1
  :l
  if (%test1 > 100) { halt }
  else {
    if (%test1 == 50) { echo -a %test1 | url -n boOboO | ;echo -a ha }
    else { inc %test1 | goto l }
  }
  */
  set %test1 1
  while (%test1 <= 100) {
    if (%test1 == 50) { echo -a %test1 | url -n boOboO | ;echo -a ha | return }
    else { inc %test1 }
  }
}


Comment and uncomment the code you want to test.

btw; using mirc 6.1