Tenho este código que cria o calendário e as checkbox dentro de cada dia do calendário:

<?php

PHP Calendar (version 2.3), written by Keith Devens

function generate_calendar($year, $month, $days = array(), $day_name_length = 3, $month_href = NULL, $first_day = 0, $pn = array()){
 $first_of_month = gmmktime(0,0,0,$month,1,$year);

 #remember that mktime will automatically correct if invalid dates are entered
 # for instance, mktime(0,0,0,12,32,1997) will be the date for Jan 1, 1998
 # this provides a built in "rounding" feature to generate_calendar()

 $day_names = array(); #generate all the day names according to the current locale
 for($n=0,$t=(3+$first_day)*86400; $n<7; $n++,$t+=86400) #January 4, 1970 was a Sunday
 $day_names[$n] = ucfirst(gmstrftime('%A',$t)); #%A means full textual day name

 $mes_pt = array('', 'Janeiro', 'Fevereiro', 'Março', 'Abril', 'Maio', 'Junho', 'Julho', 'Agosto', 'Setembro', 'Outubro', 'Novembro', 'Dezembro');

 list($month, $year, $month_name, $weekday) = explode(',',gmstrftime('%m,%Y,%B,%w',$first_of_month));
 $weekday = ($weekday + 7 - $first_day) % 7; #adjust for $first_day
 //$title = htmlentities(ucfirst($month_name)).'&nbsp;'.$year; #note that some locales don't capitalize month and day names

 $title = htmlentities(ucfirst($mes_pt[(int)$month])).'&nbsp;'.$year;

 #Begin calendar. Uses a real <caption>. See http://diveintomark.org/archives/2002/07/03
 @list($p, $pl) = each($pn); @list($n, $nl) = each($pn); #previous and next links, if applicable
 if($p) $p = '<span class="calendar-prev">'.($pl ? '<a href="'.htmlspecialchars($pl).'">'.$p.'</a>' : $p).'</span>&nbsp;';
 if($n) $n = '&nbsp;<span class="calendar-next">'.($nl ? '<a href="'.htmlspecialchars($nl).'">'.$n.'</a>' : $n).'</span>';
 $calendar = '<table class="calendar">'."\n".
 '<caption class="calendar-month"><h1><center><strong>'.$p.($month_href ? '<a href="'.htmlspecialchars($month_href).'">'.$title.'</a>' : $title).$n."</strong></center></h1></caption>\n<tr>";

 if($day_name_length){ #if the day names should be shown ($day_name_length > 0)
 #if day_name_length is >3, the full name of the day will be printed
 //foreach($day_names as $d)
 //$calendar .= '<th abbr="'.htmlentities($d).'">'.htmlentities($day_name_length < 4 ? substr($d,0,$day_name_length) : $d).'</th>';

 $calendar .= "<th bgcolor='silver' align='center'>Domingo</th>";
 $calendar .= "<th bgcolor='silver' align='center'>Segunda</th>";
 $calendar .= "<th bgcolor='silver' align='center'>Terça</th>";
 $calendar .= "<th bgcolor='silver' align='center'>Quarta</th>";
 $calendar .= "<th bgcolor='silver' align='center'>Quinta</th>";
 $calendar .= "<th bgcolor='silver' align='center'>Sexta</th>";
 $calendar .= "<th bgcolor='silver' align='center'>Sábado</th>";

 $calendar .= "</tr>\n<tr>";
 }

 if($weekday > 0) $calendar .= '<td colspan="'.$weekday.'">&nbsp;</td>'; #initial 'empty' days
 for($day=1,$days_in_month=gmdate('t',$first_of_month); $day<=$days_in_month; $day++,$weekday++){
 if($weekday == 7){
 $weekday = 0; #start a new week
 $calendar .= "</tr>\n<tr>";
 }
 if(isset($days[$day]) and is_array($days[$day])){
 @list($link, $classes, $content) = $days[$day];
 if(is_null($content)) $content = $day;
 $calendar .= '<td'.($classes ? ' class="'.htmlspecialchars($classes).'">' : '>').
 ($link ? '<a href="'.htmlspecialchars($link).'">'.$content.'</a>' : $content).'</td>';
 }
 else

 $calendar .= "<td bgcolor='#F5F5F5' align='center' data-semana=''><center><font size='2px'/>
 <input type='checkbox' name='arrachar[$day][dia]' value=$day> $day <br />
 <input type='checkbox' name='arrachar[$day][OpcaoA]' value='Peq. Almoço'> Peq. Almoço <br />
 <input type='checkbox' name='arrachar[$day][opcaoB]' value='Almoço'> Almoço <br />
 <input type='checkbox' name='arrachar[$day][opcaoC]' value='Almoço Dieta'> Almoço (Dieta)<br />
 <input type='checkbox' name='arrachar[$day][opcaoD]' value='Lanche'> Lanche<br />
 <input type='checkbox' name='arrachar[$day][opcaoE]' value='Jantar'> Jantar<br />
 <input type='checkbox' name='arrachar[$day][opcaoF]' value='Jantar Dieta'> Jantar (Dieta)</font></center></td>";

 }

echo "<input type='submit' name='submit' value='Marcar'>";
 echo "</form>";

 if($weekday != 7) $calendar .= '<td colspan="'.(7-$weekday).'">&nbsp;

 </td>'; #remaining "empty" days

 return $calendar."</tr>\n</table>\n";

}

 date_default_timezone_set('Europe/Lisbon');

 $dates = date('Y/m/d');
 $hoje = getdate(strtotime($dates));

 //Monta o calendário
 if(isset($_POST["data"])){

 list($dia, $mes, $ano) = explode('/', $_POST["data"]);
 echo generate_calendar($ano,$mes,$dia);

 } else {

 echo generate_calendar($hoje["year"], $hoje["mon"], $hoje["mday"]);
 }

?>

	O meu problema é que não consigo inserir o valor das checkbox que selecciono na tabela da base de dados.

	 

	A minha tabela na base de dados:

CREATE TABLE `marcacao` (
 `Id` int(11) NOT NULL AUTO_INCREMENT,
 `arrachar` varchar(255) COLLATE utf8_unicode_ci NULL,

 PRIMARY KEY (`Id`)
) ENGINE=InnoDB AUTO_INCREMENT=0 DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;