If you're going to use dialog -x in both if statements, why both? and if you have the target as 2,3 - you don't really need a if/if, if/else would be fine.. and you never need to use / in remotes...

on *:DIALOG:PM:SCLICK:2,3:{
  dialog -x PM PM
  if ($did == 2) {
    query %pmnick PM Accepted!
  }
  else {
    msg %pmnick I am sorry %pmnick $+ . I have chosen to deny your PM. If you continue to try to PM me I will /ignore you. Have a nice day!
    .close -m %pmnick
  }
}