Most likely it has been closed by the peer already. (From a pure logic point of view, it is also possible that your file descriptor is a bad one anyway, due to other programming errors)

Following piece of code demos this situation:

use strict;
use IO::Socket;
use threads;

$| = 1;

threads->create(\&server);
my $socket = IO::Socket::INET->new(Proto => "tcp", PeerAddr => "localh
+ost", PeerPort => 7001) || print "Socket creation error: $!\n";
sleep(5);
print "about to close socket on client side\n";
close($socket);
print "closed socket on client side\n";
print $!;

sub server {
    my $server = new IO::Socket::INET(Proto => "tcp", LocalPort => 700
+1, Listen => 5)
          || die "failed to establish socket\n";
    my $client = $server->accept;
    sleep(1);
    print "about to close socket on server side\n";
    close($client);
    print "closed socket on server side\n";
}
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