The other monks have made suggestions to add 'use warnings', add 'use strict' to your script.

Just want to point out that you can have a look at your Apache error.log to see what might be the cause of the error. And also you can also insert a few print statements to check your $month variable, and run your perl script on the command line. If it doesn't run on the command line, it will not run on the Web server.

The following is a more Perl-ish way to retrieve the month.

#!/usr/bin/perl -w
use strict;

my $timediff = 1;   # 1 hour in the future
my $month = (localtime(time+$timediff*3600))[4]   # month
             + 1;              # we need to add 1 to month

print "Content-type: text/html\n\n";

if ($month==11)
{
    local $/;
    open (FILE, 'hours.txt');
    print <FILE>;
    close FILE;
}
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