Problema actualizar datos

[una_xikilla]

Código HTML:

 <table width="100%">
        <!--DWLayoutTable-->
        <tr valign="top">
          <td width="200" height="286" rowspan="5" align="left"><img src="imagenes/menuRegistro3.jpg" width="200" height="286" /></td>
          <td width="1" height="100%" rowspan="5" align="left" bgcolor="#000166"><img src="transparent-wedge.gif" width="1" height="100%" /></td>
          <td height="43" colspan="2" align="left" valign="middle" class="tituloRegistro"><img src="imagenes/estudios.PNG" width="42" height="42" /> ESTUDIOS</td>
        </tr>
        <tr valign="top">
          <td height="2" colspan="2" bgcolor="#FF0000"><img src="transparent-wedge.gif" width="100%" height="2" /></td>
        </tr>
        <tr valign="top">
          <td height="40" colspan="2" valign="middle" class="TextoNormal"><strong><span class="Estilo5">&gt;&gt;</span> Estos son tus estudios acad&eacute;micos. </strong></td>
        </tr>
        <tr valign="top">
          <td height="164" colspan="2" align="center" valign="top" class="TextoNormal"><form id="form1" name="form1" method="post" action="meterExperiencia.php">
            <table width="100%" border="1" bgcolor="#FFFF66">
              <tr bgcolor="#99FF00">
                <td width="17%" align="center" bgcolor="#FFFF66" class="FuenteRegistro"><b>PERIODO</b></td>
                <td width="20%" align="center" bgcolor="#FFFF66" class="FuenteRegistro"><b>T&Iacute;TULO</b></td>
                <td width="23%" align="center" bgcolor="#FFFF66" class="FuenteRegistro"><b>ESPECIALIDAD</b></td>
                <td width="14%" align="center" bgcolor="#FFFF66" class="FuenteRegistro"><b>CENTRO</b></td>
                <td width="16%" align="center" bgcolor="#FFFF66" class="FuenteRegistro"><b>MODIFICAR</b></td>
                <td width="10%" align="center" bgcolor="#FFFF66" class="FuenteRegistro"><b>BORRAR</b></td>
              </tr>
			  
			   <? $Nif=$_POST['Nif'];  //$Nif="71287936B";  
          //echo "ESTO ES EL DNI ";
          //echo  "<BR>";
          //echo $Nif;
     ?>
			  <input type="hidden" value=<?php echo $Nif;?> name="Nif">
                   <?

include("conexion.php");

$sql="SELECT * FROM candidatoestudio3 WHERE nifCandidato='$Nif'"; 

$result=mysql_query("$sql",$conexion) or die(mysql_error());

echo "<table border = '1' bgcolor='#FFFF66' width='100%'> \n";

if(mysql_num_rows ($result) == 0){

echo "<td align='center' width='23%'>Sin periodo</td> \n";
	echo "<td align='center' width='15%'>Sin titulo</td> \n";
	echo "<td align='center' width='21%'>Ninguna</td> \n";
	echo "<td align='center' width='12%'>Ninguno</td> \n";
	echo "<td width='16%' align='center'><b><img src='imagenes/iconoModificar2.gif' width='29' height='27' /></b></td> \n";
	echo "<td width='13%' align='center'><b><img src='imagenes/papelera.gif' width='22' height='26' /></b></td> \n";
	echo "</tr> \n";
}
else{

while ($row = mysql_fetch_row($result)){
	
	$p=$row[3];
	$j=$row[1];
    $t=$row[2];

//echo $j;
$sql2="SELECT * FROM estudio WHERE idEstudio='$j'"; 
$result2=mysql_query("$sql2",$conexion) or die(mysql_error());
while ($row2 = mysql_fetch_row($result2)){
	//echo "<td>$row2[0]</td> \n";
    //echo "<td align='center' width='23%'>$p</td> \n";

    echo "<td align='center' width='17%'>$t<br>$p</td> \n";
	echo "<td align='center' width='20%'>$row2[1]</td> \n";
	echo "<td align='center' width='23%'>$row2[2]</td> \n";
	echo "<td align='center' width='14%'>$row2[3]</td> \n";
	echo "<td width='16%' align='center'><a href='modificar_estudios.php'><b><img src='imagenes/iconoModificar2.gif' width='29' height='27' border='0'/></b></td> \n";
	echo "<td width='10%' align='center'><b><img src='imagenes/papelera.gif' width='22' height='26' /></b></td> \n";
	echo "</tr> \n";
}
}}
//echo "</table> \n";
?>
              
              <tr>
                <td height="40" colspan="6" align="center"><input name="AnadirEstudios" type="button" class="TextoNormal" id="AnadirEstudios" value="A&ntilde;adir estudios" onclick = "location='meterEstudios.php'"/></td>
              </tr>
            </table>
                 <table width="100%">
              <tr>
                <td width="79%" align="center" valign="bottom"><img src="imagenes/guardar.PNG" width="288" height="32" hspace="150" /></td>
                <td width="21%" align="center" valign="bottom"><input name="image" type="image" src="imagenes/siguiente.PNG" /></td>
              </tr>
            </table>
			</form>		  
        </tr>
      </table>