error con javascript

[jagf820612]

la llamada a addrow esta en esta parte

Código:

<p>TABLA DE GASTOS </p>

<form id="form" name="form" action="<?php echo $_SERVER['PHP_SELF'];?>" method="post" onsubmit="asigna()">


  <table width="397" border="1" cellspacing="1" bordercolor="#000000" id="tabla" align="center">
    <tr colspan="13" align="left">
      <td align="center"><font color="#000000" size="3"><b>AGREGAR O ELIMINAR</b></font></td>
      <td align="center"><font color="#000000" size="3"><b>CODIGO MINA</b></font></td>
      <td bgcolor="#FFFFFF">	 
	  <?php 
echo"<select name=mina id=nombre_dado>"; 

$sql="SELECT Codigo_mina FROM minas"; 
$result=mysql_query($sql); 
$i=0; 
while ($row=mysql_fetch_row($result)) 
{ 
echo "<option value=".$row[$i].">".$row[$i]."</option>\n"; 
} 
echo "</select>"; 
?> 
	  
	  </td>
    </tr>
    <tr align="center">
      <td valign="top"><input type="button" name="b1" value="[+]" onClick="addRowX()">
          <input type="button" name="b2" value="[-]" onClick="borrar()"></td>
      <td><p><font color="#000000" size="1">FECHA</font></p>
          <p><font color="#000000" size="1">(AAAA-MM-DD)</font></p></td>
      <td><font color="#000000" size="1">DETALLE</font></td>
      <td><font color="#000000" size="1">CANTIDAD</font></td>
      <td><font color="#000000" size="1">VR UNITARIO</font></td>
      <td><font color="#000000" size="1">IVA</font></td>
      <td><font color="#000000" size="1">TOTAL</font></td>
      <td><font color="#000000" size="1">TIPO DE GASTO</font></td>
    </tr>
    <tr>
      <td bgcolor="#FFFFFF"></td>
      <td bgcolor="#FFFFFF"><input type="text" size="10"name="fecha_1"/></td>
      <td bgcolor="#FFFFFF"><input type="text" size="25" name="deta_1" /></td>
      <td bgcolor="#FFFFFF"><input type="text" size="4" name="cant_1" value="" /></td>
      <td bgcolor="#FFFFFF"><input type="text" size="7" name="vunit_1" value="" onBlur="multiplica(this.form)"></td>
      <td bgcolor="#FFFFFF"><input type="text" size="6" name="iva_1"/></td>
      <td bgcolor="#FFFFFF"><input type="text" size="7" name="total_1" /></td>
      <td bgcolor="#FFFFFF"> 
	  <?php 
		echo"<select name=tipg_1 id=nombre_dado>"; 

		$sql="SELECT Tgasto FROM tipos_de_gastos"; 
		$result=mysql_query($sql); 
		$i=0; 
		while ($row=mysql_fetch_row($result)) 
		{ 
		echo "<option value=".$row[$i].">".$row[$i]."</option>\n"; 
		} 
		echo "</select>"; 
		?>
	  </td>
      <input type="hidden" name="var_cont" value="evento1">
    </tr>
  </table>