I know this is an old question but I ran into the same issue and could not find the answer...

As far as I can tell, the error basically tells you that the "open" command was not successful and you are still trying to execute functions anyway (e.g. login, cmd). Below is a code snippet that should prevent this error in the future:

my $t = new Net::Telnet (Timeout => '30',
                        Errmode => 'return',
                        );
my $openResult = $t->open("$remoteHost");
  if ($openResult eq 1){
    my $loginResult = $t->login($username, $password);

    if ($loginResult eq 1){
      @lines = $t->cmd("your_command_here");
    } else {
      $lines[0] = "Error logging into device: '" . $t->errmsg . "' \n"
+;
    }
    $t->close;
  } else {
    $lines[0] = "Error connecting to device: '" . $t->errmsg . "' \n";
  }
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