use already executes at the same time as BEGIN. So while moving CGI::Carp higher is good, there's no need to use BEGIN. 
#!/usr/bin/perl 
# consent.cgi
use CGI::Carp 'fatalsToBrowser';

use strict;
use warnings;
use CGI qw(:standard);
use Fcntl ':flock';
...

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In reply to Re^2: a classic : 'Premature end of script headers' problem by ikegami
in thread a classic : 'Premature end of script headers' problem by hmbscully

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