Well the following worked fine for me:

#!/usr/bin/perl  
use Net::Telnet; 
$telnet = Net::Telnet->new('192.168.1.65');

print "Login Name : "; 
$HOST = <STDIN>; 

print "Password : "; 
$USER = <>; 

$telnet->login($HOST,$USER) or die print "can't access server"; 
@ls = $telnet->cmd('ls');
for(@ls){print;}
[download]

I do not have the Term::ReadKey module installed on my system so I removed that. There could be your problem. Or at least I had no problem not using this module and that was the only difference between your code and mine. It would also be a good idea to chomp your variables before using them incase a user enters a whitespace at the end of their user or pass or if a newline sneaks through somehow.

Edit:

Ok I installed that module to try and give you some better advice but alas mine runs perfectly.

#!/usr/bin/perl  
use Net::Telnet;
use Term::ReadKey;
$telnet = Net::Telnet->new('192.168.1.65');

print "Login Name : "; 
$HOST = <STDIN>; 

ReadMode("noecho",STDIN); 
print "Password : "; 
$USER = <>;
print "\n"; 
ReadMode("original",STDIN); 

$telnet->login($HOST,$USER) or die print "can't access server"; 
@ls = $telnet->cmd('ls');
for(@ls){print;}
[download]

Could it be an issue with the telnet server? Does the second user you are trying actually exist on the system?