my $err = join "\n", map { "Error $_<br>" } 0..100;

my @errs = split /<br>\s*/, $err;
$err = qq!<table width="100%">\n!;
for ( my $i=0; $i<@errs; $i+=3 ) {
    $err .= sprintf "<tr><td>%s</td><td>%s</td><td>%s</td></tr>\n", 
                map { defined $_ ? $_ : '' } @errs[$i..$i+2];
}
$err .= "</table>\n";
print $err;